THE ROMAN AQUEDUCT OF GIER
Jean-Claude Litaudon © 2002
TRAIANVS © 2002
The foundation of Lyon ( Lugdunum) and the historic context :
For Pline the Old :"it was built (the city) in the country of Ségusiens which were free people" as this author ensures it:"segusiani liberi in agro quorum colonia Lugdunum" (Natural History, 4, XXXII), which was to be indeed the case before this part of Gaules is reduced in province and prone to the Romans...
"what we know more about the foundation of Lyon, by whoever it was done, it is that were the inhabitants (commercial?) Romans of Vienna who had been driven out of their city by Allobroges into 62 before J.C, which created Condate, quote between the Rhone and the Saone ", to the confluence of the tumultuous Rhone (Rhodanus) and the quiet Saone (Arar), us says on his side Dion Cassius (XL, VI, 50, 4).
But it is into 43 before Jesus-Christ (the year which followed the assassination of the winner of Alésia, Jules César), that one of its lieutenants, Lucius Munatius Plancus (the same one which created Augst Raurica in Switzerland), the city of Lyon founded to which it gave his name besides, Colonia Copia Felix Munatia Lugudunum; (the two etymologies generally suggested for this name with Latin ending of Lugdunum, are: the mount of the corbels and the mount of Lug God, tell us C Germain of Montauzan in its work "the ancient aqueducts of Lyon, 1909).
Upon the departure, the city profited from the statute of Roman colony; the emperor Claude (41-54 ap. J.C.), of which we will speak again in connection with the dating of the aqueduct, native of the aforementioned city, gave him then the name of "Colonia Copia Claudia Augusta Lugudunum".
Gaule "hairy" at that time, was then divided in three provinces: Gaule Aquitaine, Celtic the or Lyons one and Gaule Belgium.
It is usually allowed today, that it is on October 9 43 before our era that was founded the city; the angle formed by the intersection of the cardo maximus and the décumanus maximus (as that was practised at that time) A made it possible to determine this date with precision.
The modest agglomerations of Condate on the edges of the Saone and of Canabae in the island of the same name to the confluence of the two rivers, on the hill of Fourvière all the usual monuments cultuels succeeded very quickly the Romans of this time. Did the rich person Roman experts also choose them to be installed on the hill or one breathed undoubtedly better than in bottom...
"Water makes city"
Pline the Old , (Natural History, XXXI, 4).
The city taking of the importance, the requirements out of water were increasingly significant. Does Amable Audin say to us in his work "Retrouver Lugdunum", which it estimates that a population of 40.000 hearts seems to him nevertheless over-estimated...
"Until year 441 of the foundation of their city, Sextus Julius Frontinus says to us says Frontin (aqueducts of the town of Rome, 4), the Romans were satisfied for their use of water which they drew from the Tiber, the wells and the sources".
The town of Lyon was fed by four aqueducts; longest of them is the aqueduct of Gier with four siphons and with the so particular coating, the opus reticulatum, one finds then the aqueduct of Brévenne with two quite distinct sections on its course, the aqueduct of Yzeron, if complex with its various ramifications and the raising of its foundation raft, and finally the aqueduct of the Gold Mount, shortest, which presents a vault in successive projections.
The aqueduct of Gier, or the Pilat Mount, the name of the solid mass where the Gier river was used for the Roman drain, is a work of approximately 86 kilometers length by including there the skirting of the valley of Chagnon; we will speak again from this problem further.
But initially which made or makes make the aqueduct of Gier? The dating of the work is like very often vague, for lack of written documents, we will also reconsider this point thereafter. It is known that at the time Roman the evergetism was often practised; this word created with the XXe century by A. Boulanger and H. Marrou, comes from the Greek and means "beneficial attitude"; for the Roman rich person, to devote part of their fortune to offer monuments, festivals etc with their coréligionnaires, and to receive in loads exchange and honors were current thing. Nevertheless, as of the republican time, the richest experts could offer particular adductions. The selective system of the distribution of water at the time Roman is well-known: In first the emperor and his house (palate, gardens etc), then public fountains, baths, horrea, gymnasia, amphitheatres (naumachies) etc; the surplus is then allotted by favour, finally there is the possibility of using the overflow of the fountains (aquae caducae).
The aqueduct, an ostentatious role:
Frontin says to us on several occasions his will that the water current is not stopped, it was thus for the Romans to make the demonstration of the domination of the man on nature, in time and space; however the passage of an aqueduct through the campaigns was inevitably to involve conflict situations between the authority which imposed it and the residents which underwent it.
Two inscriptions in Gaule Narbonnaise report the gift by évergètes passage of an aqueduct in their property; for the vicus of Albens, Sennius Sabinus gives the right to lead water in straight line through its grounds (C.I.L. XII, 2494); In Vienna, it is the mention of two magistrates offering of new water to the city as well as the course of this water through their funds (C.I.L. XII, 1882-1889).
The cost of such monumental works was such as sometimes richest took part only in part of work, or a section of aqueduct. See for example the aqueduct of C Sextilius Pollio in Ephèse (C.I.L. III, 424), where it is known as "that C Sextilius Pollio, Offilia Bassa, his wife C Offilius Proculus, her son, and their other children, joined together their resources to build this bridge" (and not the totality of the work)!
Denis d' Halicarnasse, historian of the first century before J.C., does not hesitate to say:"For me, at the row of three more splendid Roman works by which appears best the size of the Empire, I place the aqueducts, the ways, then the sewers, not only because of their utility, but also because of the expenditure which they involved".
Frontin, (XVI), is him as much emphatic:"To the masses so many and if necessary of so much of aqueducts, thus compare pyramids which are not used obviously for nothing or the works Greeks, useless, but celebrated everywhere".
Profile of the work:
"the oldest collective adduction seems to be that of Jerusalem; it probably dates from - XIe century. Assyriens, Greeks, then Etrusques had preceded the Romans in the study and the development by the hydraulic systems "(Jacques Bonin, water in antiquity; hydraulics before our era; éd. Eyrolles, 1984).
The ground in the upstream part of the aqueduct of Gier is very broken (department of the Loire), it then levels on what is called the plate mornantais, as of the crossing of the river "Bozançon" which is used as administrative limit between this department and that of the Rhone; there remain some valleys of which most significant are crossed out of siphon before arriving to Lyon.
The water run-off is done by gravitation (except of course in the passing out of siphon or it is in pressure).
But, that the word "aqueduct wants to say"?
The etymology of the word provides us his answer: it is a formed Latin word of aquaeductus, of aqua (ae, F; the water) and of ductus word derived from ducere which wants to say to lead. The aqueduct term thus indicates a work intended to lead water.
Particular characteristics of the work:
The aqueduct of Gier is a work built, rectangular, composed of a foundation raft, two oven walls, a vault; the height is 1,60 m under under-surface; the archstones constituting the semi-circular vault measure except exception from 30 to 40 cm length. Its width from 0,55 to 0,57 m between the oven walls (vertical walls) is almost always covered with hydraulic coating on a 1,30 m height, it acts of the famous Roman broken tile; this one making up of lime, sand and crushed bricks then is applied in increasingly fine layers, increasingly smoothed to facilitate the drainage duct, it acts of the opus signinum, often red, or rosy color when it was in contact with the atmospheric agents; the thickness of this coating is generally 2 to 3 cm; the horizontal part, the foundation raft, is it also covered with this mixture (12,5 cm minimum). With the junctions of the vertical and horizontal parts one finds plaster fillings or quarter round in order to reinforce the etancheity of the work.
As the majority of the hydraulic works, the aqueduct of Gier was generally produced in a trench from 2 to 3 m of depth, embanked then; the drain generally follows the level lines, means of transport more running, because the least expensive; it is what explains the length of the work compared to the point of arrival generally located at a quite less distance to flight of bird. In addition water is thus (in theory?. to see the work of Nimes upstream Bridge of Gard) protected from possible covetousnesses farmers or other profiteurs along his course, and it remains at a pleasant temperature. The aqueduct when the profile of the ground requires it ground fate and appears then on a wall, known as wall-carrier (substructio) which supports the drain. On the aqueduct of Gier in particular, when the height of the wall is about to exceed 3 meters in height, one has recourse to arches, the aqueduct bridges (the opus arcuatum).
Characteristics of the aqueduct of Gier, materials constitutive:
All the parts except ground of our work are covered of a type of apparatus known as "réticulé" (opus reticulatum), almost single characteristic for a Roman aqueduct, since one knows only another hydraulic work built with this type of apparatus, it acts of the aqueduct of Minturno, located close to Naples, in southern Latium. This type of construction is composed of square stones laid out in rhombus, with 45° thus; each face being able to measure from 7 to 11 cm on side, the length which is decreasing, generally lying between 20 and 25 cm; these cut stones are out of various materials, generally collected in priority near the work, but arriving sometimes from fort far; schists, granites, limestones, stones of Couzon; in the Lyons part of the work one rather often finds feldspar associated with granite (D. Litaudon, Revue G.A.F.J., N° 4, 2000). One particularly finds brick in this same sector on the Lyons part of the work, either in the arcs, in alternation with stone, or in levelling courses (left horizontal, separating the covered parts of réticulés) on the arches and bridges, it is then about the opus mixtum.
The valleys are circumvented by bridges (40) or crossed using bridge-siphons when the manufacturers have recourse to the type of works had which are the siphons. The aqueduct of Gier comprises four of them, and like the other Lyons aqueducts have some respectively, two for the aqueduct of Yzeron, two for the aqueduct of the Mount of Gold and large for the aqueduct of Brévenne, the Lyons area was thus as of the Roman time a true crossroads of siphons!
"the siphon appeared for the first time on a water conveyance in Jerusalem, but they are the Greeks who multiplied it in Greece, Sicily, Spain and minor Asia starting from the beginning of IIe century before our era", (D. Hill; With history of engineering...; 1984).
It acts here of the type of siphon says reversed siphon; water arrives in the tank located upstream, this monument is called reserve of hunting. Water arises from it by several lead pipes (fistulae) (3 m length each one), to divide the flow and thus the force of water. These pipes are supported on a called built part crawling before joining the ground, where they were undoubtedly buried to the arrival on a bridge-siphon, the belly of the work (libram, libramentum), this last decreasing the drop height of water (the arrow) and thus the pressure. The elbow (geniculus) caused by the abrupt break of slope was the most fragile place of the siphons; the crossed valley, the pipes went up other side to another tank, said reserve of escape, located low than the first, and finally water found the channel normally built and continued its course until its destination.
The tunnels, eleven for the aqueduct of Gier, are works made necessary when the ground is unstable for crossing in cornice of a valley or to shorten the way of the drain; After a marking on the surface of the layout of the channel, the workmen began work with the two opposite sides; it was desirable that the two galleries then meet (the aqueduct of Gier comprises like many works having rather long tunnels, a masterly error of layout; wells (putei) were used for the spoil removal, ventilation, and the calculation of the levels; those being sometimes with astonishing depths.
On the aqueduct of Gier, in trench, tunnel, wall-carrier, and on the arches one finds glances (covered by two flagstones with cover of almost 350 kilos each one!), glances located almost always at an interval of two actus from/to each other! There one finds the application almost perfect of the principle published by Vitruve, (VIII, 6), taken again by Pline the Old one, (Natural History, XXXI, 31;"the slope of water must be at least a quarter of inch percent feet; if it passes in tunnel, one will need glances both actus "(if cuniculo ueniet, in binos actus lumina ess debebunt); one also finds in alternation generally large and a small glance; but there are nevertheless anomalies, we will return there; briefly let us recall that the actus measurement 120 feet Roman of 0,296 m, (with variations sometimes, a little more than 30 cm in our country).
More than thousand glances on the aqueduct of Gier, it is there a formula which J Burdy employed, (the Roman aqueduct of Gier, 1996), while realising of the almost normality of the intervals of these glances or well on the aqueduct of Gier; this characteristic had been noticed for the very first time by the geometrician Noël Delorme in 1950. In June 2001, 89 glances were listed on the aqueduct of Gier.
In 1999, the advisability was given of checking an assumption; with knowing the great glances (thus broader than the channel) did not justify themselves that if they were provided with vats of stop of the impurities; (Jean-Claude Litaudon, Review of the G.A.F.J., N° 3, 1999). And yet useless does it seem? Opinion shared by Hubert Chanson, (private correspondence, to see bibliography), which thinks that the existence of these widened glances and shallow arches involves an increase in pressure losses, which wants to say a loss of energy of the flow, involving a reduction of the maximum capacity of the aqueduct. Indeed why as many these great glances, almost always with a flattened bottom, whereas the impurities can come only by the means of roots or movements of ground having made them fall into the drain or then by the interstices between the flagstones from covers. But was it necessary to do as many these vats of it, in theory thus nearly 500? A vat of stop of impurities located every 300 meters would have been largely sufficient seems it. Most significant is to prevent, therefore upstream tanks of hunting of the siphons the arrival of solid matters in the pipes, matters which, not being able to go up, will accumulate at the low point, will decrease the flow initially, and then will seal the pipes completely and thus will immobilize the siphon.
Course of the work:
The hydrant on the river Gier was made with the dimension 405 meters and after a unevenness of 105 meters approximately the arrival was done in a reserve of distribution at the point highest of the hill of Fourvière.
It is to a few hundred meters in the north of the building religious of the Marist brothers, known as the Hermitage, in Saint-Chamond (the Loire), whom this hydrant was to be, which is so far only known hydraulic work.
There was to be a large basin at the beginning of the work acting of decantation and regulation; Gier, which will be useful many centuries later with steeping of the weapons, appeared a very pure water, not leaving any trace on the oven walls (!)."a basin, of about circular form, marked clearly and limited the site of this basin" tells us C Germain of Montauzan (already quoted). The drain moving then towards the North-East was met on nearly 450 m to the locality "Varizelle" with Saint-Chamond, during preliminary work to the construction of the carpark of a supermarket into 1993).
Its arrival in this place was done by a tunnel, in which we had the occasion to see the specus personally builds entirely out of bricks.
Had the Romans thought that built in the tunnel itself, the drain would be thus protected from the external aggressions? One had already seen this type of construction in 1975 on the commune of Sainte-Foy-les-Lyon (J Burdy, 1996). However in is the other tunnels, the construction of the aqueduct out of stones? Then, repair?
While following the layout of the channel for this work period, we located and measured 6 inspection chambers, undoubtedly 7, which had enabled us to already determine the alternation of small and great glances in the upstream part of the work.
Unfortunately, of the tunnel, of the glances, plus nothing today visible, all was destroyed...
Let us note what in this first part of the course of the drain, eight bridges left some visible traces today and note that on the five best preserved, there was indisputably rebuilding? It is not known if this is due to problems of seismicity or movements of ground. Are carboniferous schists and coarse sandstones numerous in this sector, that gives relatively unstable grounds...
The work crossed then the following valley, with the locality Bridge-Nantin, by a very long bridge, the first of a series of 40 as we already said."a 200 meters length aqueduct bridge, whose remains were still used at the time of our operations to maintain the road Saint-Etienne in Lyon"; (alas!) the quotation is of Paul De Gasparin;"Memories..." 1856; page 210, 3rd subparagraph).
The drain curves then in the countryside, meets valleys or small valleys which will be crossed on bridges or culverts before arriving towards a point of the course, very interesting, disappeared unfortunately today, with the Couttange locality; at this place there were two bridges, in parallel, the second replacing the first for crossing of a small valley (J Burdy, 1996); the case is well-known on the aqueduct of Frejus, with four identical cases; to see on this subject Internet site of Vito Valenti on TRAIANVS. One reconsiders the problems already referred to above in connection with the state of the ground in this first part of the course.
A few kilometers further the drain presents a single type of construction in its realization. Indeed, a trench cut directly in the rock was used itself as aqueduct, without interior construction of oven walls seems it; on nearly 500 m, in the conglomerate, the channel is dug in such way that sometimes the edges of the rock meet almost, forming a pretence of tunnel; on each side of the channel, two significant shoulders were to be used as supports with the built vault which was thus protected twice.
Finally the aqueduct arrives at the entry of the valley of Durèze, of the name of the river which runs there. It is what is called the by-pass Chagnon (village at the bottom of the valley); part of the drain borrows a siphon from the Leymieux locality and crosses the valley directly; another drain made it it full rotation of the valley (more than 11 kilometers!) Both met then other side. With regard to the siphon, the first of the four of the aqueduct of Gier, the reserve of hunting is well preserved (as besides the three other tanks of hunting of the other siphons, with contrario the reserves of escape, them, have all disappeared); the interior of the building is composed of a room arched 6,45 m length for 2,25 m broad; each one of these buildings was surmounted of an inspection chamber; 9 lead pipes whose openings of exit are still quite visible for 7 of them went down towards the bottom from the valley, supported as of the exit of the tank by one crawling (plane tilted built). A tenth hole was stopped by the Romans themselves (fear of seeing the work désarmorçer in period of low water level?)
These pipes measured 23 cm outside for a 2,5 cm thickness approximately and a 3 m length; (the pipes of the siphon of Trinquetaille in Arles, visible with the museum of the city, are provided with barbs to avoid slipping).
Of length a 900 m each one, put end to end, they were pressed on the bridge-siphon located at the bottom of the valley before going up to the reserve of escape placed at a level lower than the reserve of upstream;
Here the height of arrow is 78 m (difference between the bridge-siphon, of 136 m length, and theoretical line of level) and the pressure loss (difference between the levels of the foundation rafts of the two tanks is 5,80 m here). According to the calculations carried out for the aqueduct of Gier alone, one will thus have needed ten thousand tons of lead for its four siphons!
"...Si the valleys are extremely long one will lead the pipes to it while going down according to the slope from the slope, without supporting them by masonry; and then it will happen that they will go extremely far in the content of the valley according to its level, who one does call belly...
...if they had not been led by this long space which is on level along the valley, they would make while going up very short, an elbow which would force water to make an effort able to break all the joints of the pipes. In this space which is called belly, it will be necessary to make suction cups by which the winds which will be locked up, can leave "(Vitruve; VIII, VII).
The part of the drain which makes it tower of the valley, crosses several small thalwegs in which one finds today any more no trace of the culverts which were to cross them. Nevertheless, it is on this part of the course that a tunnel called is located the "Cellar of the Priest". Located at hillside, the cuniculus (called thus as rabbits which one recognized undeniable qualities of sapper, of minor) met a rocky outcrop; did the Roman engineers choose to cross it rather than to circumvent it (unstable ground always?) It is in this tunnel dug in the rock, 83 meters length and 1,60 to 1,80 m of width, for an average height of 2,20 m, which was built the aqueduct. Today still one notices the traces of the blows of peaks, of points of the workmen. Small niches located at height of face were to accomodate the oil lamps necessary to light. With a score of meters of the entry of the tunnel is the aqueduct itself, in a perfect state of conservation and which one can use to cross the mountain.
In 1991, the Spéléo-Club of Villeurbanne, helped of some volunteers of the area, undertook "to remove obstructions from" another tunnel, located further and which was then stopped, the tunnel of Fontanes, on the commune of Saint-Martin-la-Plaine;.long of more than 200m, this tunnel located up to 12 m of depth, offers still today interesting elements on the principle of digging of the tunnels at the time Roman: several consecutive glances or wells, one of them is entirely visible by lower part being free of any cut; boards of the formwork of the vault (three), "forgotten" on the spot, as well as small clay platforms "built" to support the lamps of the workmen, and especially "the error" of layout, quite visible with the connection of the two drains; this connection coarsely cut in the rock, joint the two galleries which as for them were built normally up to now. One thinks here of the famous inscription of Vernier Datus (C.I.L. VIII, 2728; I.L.S. 5795), which to feed Béjaïa, city Algerian (formerly Saldae), about the middle of the second century after J.C., determined the layout of the tunnel having to feed the city, tunnel being 428 m long for a maximum depth of 86 meters; the still visible inscription today, reports misfortunes which arrived at the drain and to its originator, before this last rectifies fortunately the layout.
In Fontanes, the error was not very significant, the workmen had to mean and realize that they were going to be missed and could thus "rectify" the layout; one also thinks of the very visible mistakes on the aqueduct of Nimes in the small valley of Escaunes, with several beginnings of sizes, abandoned then.
The valley of the brook Bozançon, separates the department from the Loire of that of the Rhone, we said it. Here the aqueduct will make the full rotation of this valley, by a turning of more than 4 km. There were eight bridges, five remain; That of Jurieux, from its low height is the only one which is currently complete; the "Bridge" of the Barns, of about thirty meters length for eight meters in height, is perhaps most beautiful of all the air works of the aqueduct of Gier; it is true that the decoration in which it is is there for much. One can make it tower of the valley, to go from one vestige to the other, and to see underground parts of the aqueduct, it is a splendid place of walk here.
At the exit of this valley, one approaches the plate mornantais. A few kilometers further, the city of Mornant is also crossed by the tunnel, longest of the course of the drain, the 825 m, and also major, 20 m at its climax!
The aqueduct moves then towards the second siphon of its course. Several hundred meters of the drain, in several sections, magnifiquement covered réticulé facing is visible to the tank of hunting of "Gerle".
The bridge-siphon which succeeds to him at the bottom of the valley had 23 arches, 210 meters length for a 21 m height; the arches which remain measure more than 7 m of width... There remains the six first and the four last; here one immediately realizes, one will also make it for the following siphon, that of Beaunant, that the arches were dug perpendicular to the work; highest, most fragile, having been filled into réticulés after initial construction by the Romans themselves. The arrow is 93 m, the pressure loss of almost 9 m.
We approach then the commune of Chaponost and its many vestiges; most spectacular are indisputably the long file of arches of the locality "the Dish of the Air". On does the 92 original arches, it remain 72 about it... Réticulés is here out of limestone and contrasts agreeably with the red of bricks. This long file of arches, which has you airs of Roman countryside, finishes while arriving at the third reserve of hunting; it is most spectacular; the arrival is to 15 m height and crawling it which goes down from there up to the level from the ground is impressive, very as much as the valley which follows, with the bridge-siphon of Beaunant, its hollowed out arches, for the lowest, others filled as we already said 270 m length, 18 m in height, to cross this 2600 m length valley, the arrow being here of 123 m!.
The aqueduct arrives then in an increasingly developed zone of the Lyons agglomeration. The fourth and last siphon, that of Trion, crossed a 600 m length valley; its arrow was 30 m and the pressure loss of 1,50 m before arriving on the hill of Fourvière. A very large cistern, on two levels, (there remains only the lower level), was supplied by the Roman drain, which was close to its terminus there.
Slope, flow, and period utilisation of the work:
The slope of the work is exceptionally regular on the course of the aqueduct, 1 mm with the meter! Only the part of the contour of Chagnon presents a weaker slope, about 0,5 mm on the upstream part. J Burdy estimates at 12.000 m3 of water per day the volume of water transported. Rappellons that the aqueduct of Gier did not leave any trace of deposit (sinter) on the walls, the height of transported water is thus not visible. Utilisation period of the work also for the same reason in the absence of deposit; it seems impossible that the Lyons aqueducts survived the great cruel invasions in IVe century, but did they still function at this time?
With were the wire of the centuries, there undoubtedly many of other barbarians...
Andre Pelletier in "History of Lyon", ED Horvath, 1990, us tells that in 1852 the prefect of the Rhone wrote to the mayor of Chaponost:"Since one discovered in the surroundings of Chaponost of the lead pipes coming from the ancient siphons, the peasants dig with the foot of the piles thinking that they will find lead everywhere where there are Roman constructions. It is urgent to put an end to this state of affair, and to redouble monitoring to make respect these monuments ".
On this subject Frontin (CXXVI), (which lived at the first century of our era), wrote already:"the greatest damage is caused by the trees of which the roots bore even the vaults and the walls of the conduits"; but causalities are multiple: in addition to was the invasions, erosion, there also the recovery of lead, source (?) of profit; possible seismic movements, and even change of mentality which involved one on-ruralisation cities at the Lower Empire.
Duration of construction, cost:
There too, the engineer as a Roman head in charge of the construction of the work not having left us documents over the duration of construction of the work, we are obliged to make comparisons with other Roman works on which we have inscriptions: It took 5 years to build Aqua Marcia (91 km) and 12 years for the 69 km length Claudia (Frontin V-ix and XIII), then the aqueduct of Gier, a dozen years? But one would not have to forget the preliminary works with the construction of the work, choice of the layout, search for materials, construction of an access path etc... etc...
No the indication either at the cost of the work: Aqua Marcia would have cost 180 million sesterces into 144 before J.C. (Frontin VII), and the aqueducts claudiens, "350 million for Aqua Claudia and Anio Novus" tells us Pline the Old one (XXXVI, 24); it is usually allowed that so at the time Roman one measures in kilometres of way cost 340.000 sesterces, one kilometer of aqueduct could cost 2 million of them! Without speaking that after construction there was maintenance...
Dating of the work:
April 27, 1887 was found near the village of Chagnon, (thus on the skirting part of the valley of the same name), a terminal of protection of aqueduct (C.I.L. XIII, 1623). In 1996, another, partially cut down by the first three lines corresponding to the imperial titulature, but whose text is identical to the first (that of Chagnon) was found in Saint-Joseph, with the limit of the departments of the Loire and the Rhone (apart from the skirting part). There were certainly to thus be others of them throughout course! Dimensions of that of "Pierre" of Chagnon 1,60 height m are for 0,60 m broad and 0,25 m thickness. The text, in Latin, is as follows:"By order of the emperor César Trajan Hadrian Auguste, to anybody the right is not given to plow, sow or plant in this space of ground which is intended for the protection of the aqueduct".
The mention of the Hadrian emperor could leave think of some that the aqueduct could be allotted to him; in fact the engraved text is one senatus-consults (auctoritas) less 11. There is not mention of the distance to respect work on both sides as it was the case on the aqueduct of Vénafro in Italy (15 feet on both sides of the sources and 5 feet around the underground channels); in less 9 another law will be promulgated insistent on the sanctions incurred in the event of infringement, but without mention of the distance to be respected.
It is known that the emperor Claude (41/54) was native of Lyon, from there to want to honour his birthplace, it has only one step there that of aucuns crossed easily in 1982 at the time of discovered on the site of the Verb Incarné (hill of Fourvière in Lyon) by the archaeologist Eric Delaval of blocks of stones, which reconstituted proved to be a basin; on did the attic of the monument appear following inscription "CLAUDAUG"?
At was the altitude of 283 m where found this monument, only the aqueduct of Gier could have fed it?
But the inscription proves only that the fountain existed at the time of Claude:
Armand Desbats of the C.N.R.S. published in Gallia, volume 55, 1998, the result of his excavations on the site of Fourvière; for him the work could date from the period augustéenne (-27 + 14).
It is thus probable that the work was built during first half of the first century after our era. Here where we are today, while perhaps waiting for a new lucky find to start again the debate on the dating of the aqueduct.
Instruments of aiming and levelling at the time Roman:
Vitruve says to us on this subject:"One bubble with diopters of the water levels or the chorobate, but it is better with the chorobate, because water diopters and levels lead to errors"; (VIII, V, I).
Vitruve was one holding of the chorobate, Héron of Alexandria abundantly details to him the use of the diopter; The length of the chorobate, six meters length, was not to prove very practical in the valleys and on the long distances.
It is necessary to announce on this subject the publication into 2001 of Mr. J T Lewis entitled:"Surveying Instruments of Greece and Rome"; the author tried out on a distance of 173 m a simple instrument by his operation, Libra aquaria; a level with water based on the principle of the communicating muds; the author known as:"Libra... to detect the small slopes of the Roman aqueducts, it must be more precise than the diopter "!
For the calculation of the right angles, the Romans used the groma.
The diopter as for it, being used to aim and calculate the angles, was a little the ancestor of our modern theodolite.
Anomalies of layout and construction:
We already announced the rebuilding of the first works of the aqueduct, then the error of layout of Saint-Martin-la-Plaine, also now let us announce the proximity to Mornant of two large glances model consecutive.
Recently, Association the Swing-plough and the Archaeological Group Drill-Jarez had the occasion to initially notice two consecutive glances of small size, of which one was stopped by the Romans themselves, followed by two successive glances great model, one of them having been there too stopped by the Romans!. The intervals separating these glances are 40 m only for the first, then after an interval of 102 m, the two following is separate only 36 m!
The higher trench:
On the first part of the work and until the limit of the departments the Rhone and the Loire (that is to say nearly 50 km), one notices regularly each time the notched rock is let see, to 14 m above the aqueduct, a trench, cut in the shape of trapezoid widened upwards.
No trace of interior construction. There A was there too with the wire of the time much of assumptions on this work; one of those which seems to us most plausible would be there to see an outline of layout; a test in nap, which could have been carried out on the basis of the upstream, and stopped when the engineers realized that this layout would be much too long and too high works including on arrival in Lyon; Rectifying their error, those traced this time the aqueduct on the basis of the point of arrival, it did not matter the exact point of the hydrant in the river Gier, only the level to be respected on the course being significant.
Lastly, we found only once an anomaly compared to the width of the specus, in the direction of a width more significant than the normal; indeed, at this place on a stone bed normally installed on the level of the oven wall is a mortar bed of 1 cm thickness with a layout of drawn joints to the point; this coating itself was then covered with the coating of usual broken tile. The width of the channel at this place is 67 cm stone with stone without coating. Why, there still mystery... One moreover...
In do the study on the aqueduct of Gier many mysteries still remain, the study and research will undoubtedly bring answers but also undoubtedly of other questions and it is so much better...
"...the aqueduct... if one evaluates with exactitude volume of water which it pours on the public places, in the baths, the swimming pools, the channels, the houses, the gardens, the properties of suburbs and if one considers also the distances covered by the water current, the raised arcs, the opening of the mountains, the filling of the valleys, one will agree that never the whole world did not present great any more wonder?". Pline the Old one; (XXXVI; 123;1er August 52).
Our conclusion will be that which Alain Malissard employed in his work, the Romans and water; ED. The Beautiful Letters;1994:
"...la force of the Romans was indeed less to invent to increase and know to use. What is specifically Roman, it is thus the multiplicity of the aqueducts, the hugeness of the distances which they made traverse with water, the abundance of the flows which they obtained and audacity of the works that they reflect in place to cross the natural obstacles "
The photographs are of Jean-Claude Litaudon except which its author is indicated.
Traduction: Isabelle CADARS (2004)
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Litaudon (Jean-Claude): various articles on the aqueduct of Gier; review of the G.A.F.J.; Saint-Etienne; 1997/1999/200/2001.
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Malissard (Alain):"Romans and water"; ED. Beautiful Letters; 1994
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