Fig. 1 Pierre-Châtel. through the Epine range and position. Artwork: P. Artru.

A Across the Rhône Discovered at Pierre-Châtel (France) Philippe Artru

Situation and historical background entrance of the gorge and a cable ferry was then in use until 1837 associated with a toll. Some administrative The 3km long, 100–200m deep Pierre-Châtel gorge is and military documents however mentioned the remnants located on the French Upper-Rhône between Geneva and of a bridge across the Rhône at the Bas-Fort site in 1723 Lyon (Fig. 1). The Rhône flows through picturesque cliffs and 1852. Roads enlargements and rocks collapses have cut in Upper Jurassic and Lower Cretaceous limestone now destroyed those remnants and it took the author three formations. Since 2003, the author has conducted a field more years to prove the bridge existence and its antiquity. research program on the main Roman roads of Savoy between the pre-Alps and the Rhône. A road, indicated The access ledge on the Antonian Itinerary and the Peutinger Table came from through the Petit-Saint-Bernard pass and then The carved ledge discovered in the cliff can be compared Lemincum (now Chambéry) heading for Vienna. Another with one existing on the Val de Fier Roman road between one leaving the precedent at Lemincum, reached the col Annecy and Seyssel some 40km north. It also presents du Chat pass and then the Rhône at Yenne upstream from strong similarities with known Roman carved passages Pierre-Châtel. The author’s previous research has shown at Ruaz in the Val d’Aoste (Italy) and the Romanche road that this was also an important road open to vehicles and east of Grenoble. To reach it, the Romans used a natural most probably heading for Lyon but no trace of it had ramp with a 10% slope but only vague remnants of the ever been found in the Pierre-Châtel gorge. In 2005, a road are still visible. The junction between the ramp and systematic survey led to the identification of a carved the ledge, which are currently 30m apart, was probably passage located on a natural ledge some 40m above the provided by a 15–20m high masonry wall, which is also river.1 This road with its typical Roman features could missing. only lead to a bridge as it stopped abruptly in the middle The ledge itself presents three carved passages and three of the cliff north of a former stronghold called the small caves, which could have been used for lodging the Bas-Fort. Past local historians had written of a legendary road caretakers in peacetime or guards when needed. bridge crossing the Pierre-Châtel gorge but only a wooden Among some interesting features are very regularly pick- bridge was attested from 1137 to 1227 at the downstream hewn striated faces and some grooves and holes suggesting

131 Fig. 3 Pierre-Châtel. Right bank remnants. Left: present condi- tion (vegetal cover partly suppressed). Right: reconstruction in Roman times. Drawing: P. Artru.

an abutment must have been standing on the bank of the river. Nowadays, the only traces left of it are high underwater steps cut in the limestone with remnants of a foundation wall.

The remnants on the right bank

On the right bank, in front of the anchoring cavity and hidden by vegetation, the author found a 12m wide trench with a flat bottom inclined at 45° (Fig. 3). The two internal sides of the trench consist of vertical 2–4m high cut faces. This 42m high trench, still intact at a height of 27m, certainly represents the foundations of a massive Fig. 2 Pierre-Châtel. Left bank remnants. Above: present con- dition. Below: reconstruction in Roman times. Drawing: P. Artru. abutment. To realize this work it was necessary to dig into a rocky ridge but the architect took care to leave a 2m the former presence of wooden lateral extensions of the wide wall of natural rock on the ridge’s west side, vertical road built initially or after a partial collapse of the ledge. on both faces. The purpose of this structure oriented at Such extensions, similar to the ‘plank roads’ of old China, 15° from the bridge axis, was most probably to support existed on the Iron Gates Roman road along the a succession of dissymmetric shoulders reinforcing the and on the Romanche road near Grenoble. downstream face of the abutment. Above water, not a single block has been left of this huge construction, The remnants on the left bank which certainly did not collapse entirely as it was strongly anchored laterally and vertically on stable limestone Just before reaching the Bas-Fort promontory, the ledge beds. All its large blocks must have been recovered at an stops abruptly above a 12m wide, 8m high, 1.5m deep unknown date after the bridge destruction. rectangular man-made cavity (Fig. 2). Its form is typical The top of the trench is barred by a 4m high masonry wall, of the cavities made to anchor a stone bridge in a steep the role of which was probably to protect those working rocky bank, but its position and its size imply a bridge on a steep and exposed site from stones falling from of exceptional dimensions. Its depth was 2–3m before particularly dilapidated limestone beds. On the lower a collapse caused by an attempt to widen the tunnel end of the abutment, hard limestone beds emerge from crossing the promontory. Above it, a rough triangular the bottom of the trench. They are cut into steps, which pediment-shaped structure, with the same axis of sym- once formed the base of a that crossed the Rhône. metry, has been carved in the cliff, probably to clean it Immediately upstream other steps cut at a 35° angle with from menacing rock pieces. the abutment front face were probably the base for an The 10–12m span of the first is deduced from the oblique wall facilitating the flow during high water and 8m height of the cavity, taking into account that the protecting the abutment. cylindrical vault thickness ought to be 2–3m according to stone usual dimensions. The level of the road was Bathymetric surveys 30m above the present road and 42m above the river low waters level (217m above sea level). Most probably this Despite the importance of the remnants found on both arch was needed for the passage of another road along banks, no ashlars from the bridge itself have been found the river, which is still visible now, circling the Bas-Fort and exploration of the river itself became necessary. The promontory. A large pier, so massive that it may be called ‘Compagnie Nationale du Rhône’ (CNR), which exploits

132 Fig. 4 Pierre-Châtel, 3D isobaths diagram of the Rhône (courtesy of CNR) with bridge position, view from upstream. Artwork: P. Artru. the hydroelectric dams and power plants on the Rhône, generously offered to do the necessary bathymetric survey with a specialized boat and team (Fig. 4). Near the Bas-Fort, the isobaths 3D diagram shows that the bottom is nearly flat at a depth of 10–13m (at low waters) and consists of pebbles. The bottom profile shows an almost continuous plateau close to the right bank, followed by an 8m near-vertical face before reaching the pebbles. On the left bank, the slope is less steep and full of collapsed natural blocks. Two-thirds of the Rhône flow are now detoured through a canal, but when the totality of the river was flowing through the gorge, it carried the pebbles away and the depth must have reached 15–17m, even by low waters, and up to 20m during centennial high waters when the flow can reach more than 2,000 3m /s. Such depths and the swift current made the building of a pier in the middle of the river impossible even if it may have been feasible to put the foundations at a depth of 5–6m in front of the pile during the summer low waters of the Roman period warmer climate.

The main vault

From the above it must be concluded that only one vault extended over the Rhône. It reached a height of 43m (including parapets) above the present winter low waters levels as determined by the access road elevation on the left bank. Total built height may have been 49m if the probable foundation wall is included (same height as the Alcántara bridge and ). The topographic Fig. 5 Pierre-Châtel. Underwater ashlars accumulations along data supplied by the CNR give a distance of 44.40m from bridge axis and downstream. Above: blocks seen from a boat one bank to the other on the bridge axis at low water. close to the right bank trench. Photos: P. Artru. Manipulation cav- ity, rough-hewn face and cornice element with heel. Below: typi- Therefore, the span there was most likely between 40 cal ashlars (1 x 0.50 x 0.50m). Photos: F. Michaud. and 45m. The still existing vault of the Pont-Saint-Martin bridge in the Italian Val d’Aoste, the largest known one in top and assuming a cylindrical design we can deduce the the Roman world, has only a 35.6m span. height of the vault base (springing): 16–19m above the The width of the deck is unknown but must have been low waters level. The length of the bridge was 114m from close to 7m as in some of the largest Roman stone the anchoring cavity wall to the top of the protection wall bridges. Assuming a 2.5m thickness of the vault at its on the right bank.

133 Discovery of large block accumulations right bank is possible and in accordance with in the Rhône precepts but not yet proven. As no voussoirs have yet been clearly identified the author cannot be sure that the During the bathymetric survey, by particularly clear main vault was made of stone. Therefore, he proposes water, the author observed several regularly cut blocks two drawings of the bridge, one with a stone arch, the near the right bank abutment base (Fig. 5). Then, two most probable, and the other with a wooden arch, all experienced divers, F. and S. Michaud, discovered tens other bridge elements being similar.2 It must have been, in of blocks about 1m in length for a 0.50 x 0.50m section any case, a mighty structure as it stood across the Pierre- and obtained convincing photographs. Some have rough- Châtel gorge landscape, some 2,000 years ago. The hewn faces and others have cavities resulting from the bridge destruction was probably due to a combination quarrying process. Typical Roman metal-joints holes, pre- of partial undermining of the left bank abutment by the hension and manipulation holes were also present as fast-running waters and an east-west fissuration of the well as a cornice element presenting a heel similar to bedrock. Similar causes have ruined many large Roman those found in the cornices of Vila Formosa and Segura bridges and without extensive works could have brought bridges (M. Durán Fuentes). The most probable source disaster to such monuments as the Pont-du-Gard or the of the blocks are Portlandian and Lower Cretaceous Alcántara Bridge. regular limestone beds, one kilometre upstream where quarrying activity during the Roman period is attested Dating the bridge from a low-relief by an unfinished sarcophagus and where R. Vinet found numerous extraction cavities on unfinished ashlars. Everything about the bridge speaks for its antiquity: the typical carved access road; the horizontal or sub-horizontal Reconstructing the bridge upper bridge surface; and above all the width, correspond to the main criteria retained by M. Durán Fuentes and Some of its dimensions like height, width, length and other authors. Other features like the exclusive use of arch span are easily deduced from field observations large limestone blocks and their morphology, the cornice, (Fig. 6. 7). Others are chosen to be compatible with the joining holes, manipulating holes and the rough-hewn Roman bridge architecture (cylindrical vault, voussoirs faces led J.-P. Paillet to the same conclusion (or. com.). visible down to the springing). It is noticeable that the Looking for some inscription, the author made a stunning arch height and span as well as the right bank abutment discovery. About 10m above the bridge’s left bank length are practically equal contributing to the bridge’s extremity, carved in the vertical cliff, a human figure was awesomeness. The presence of a small third arch on the discernable in the centre of a 1.8 x 1.4m square cavity.

low-relief

carved right bank road road

anchorage cavity

collapsed slice of cliff

left bank road

protecting wall upstream protecting wall abutment pier foundation wall present depth

pebbles 0 5 10 15 20 m possible depth in Roman times

Fig. 6 Pierre-Châtel. Tentative bridge reconstruction with a stone main arch (from upstream). Drawing: P. Artru.

134 Despite the injuries of time and the calcitic encrustation that smoothed its features, one can still identify the upper half of a man dressed as a high-ranking Roman official, most likely an emperor. His paludamentum is sustained by his right forearm. 6m below this square cavity forming a sort of medallion there is a narrow platform where scaffolding was erected to make the sculpture, with beam holes still visible as well as a small man-made cavity that may have been used for offerings. A sort of staircase, partially cut in the cliff, connected the platform to the bridge extremity.

The bridge and the Roman roads network Fig. 7 Pierre-Châtel. Tentative reconstruction of wooden main arch (from downstream). Drawing: P. Artru. The discovery of the remnants of a bridge whose main arch was one of the three highest and presumably the widest known to have been built by the Romans has far- komplett abgebrochenen, 12 m breiten Widerlagers in- reaching implications. Apart from being the first Roman terpretiert. Taucher fanden im Rahmen eines bathymetri- bridge on the Rhône described between Vienna where schen Surveys große Anhäufungen von Quadern entlang two Roman bridges have been identified3 and Geneva, it der Brückenachse. Die antike Zuordnung der Brücke was also second only to the Pont-du-Gard in its size in ergibt sich aufgrund ihrer Form, der Dimensionen, der Roman Gaul. It also points to the importance of the road Zugangsstraße, des Fehlens von Mörtel, der Größe und coming from Italy and going towards Lyon, the largest Morphologie der Quader sowie deren unterschiedlichen town in Roman Gaul where it has always been difficult Aushöhlungen. Einige grob in Stein gehauene Gesichter to establish and maintain a bridge on the divagating und ein herausgearbeitetes Gesims sind weitere Kriteri- Rhône. The Peutinger Table itinerary joining Vienna and en, ebenso ein ziemlich beschädigtes Flachrelief ober- Geneva via Augustum, Etanna and Condate crosses the halb des Brückenendes, welches eine römische Gestalt Rhône between Augustum and Etanna. This also may be zeigt. Die Brücke führte die römische Straße von Italien accepted as a valid Roman attestation for the bridge. The über den Kleinen St. Bernhard und Chambéry (Lemin- author’s recent field research suggests placing Etanna cum in den Itinerarien) westwärts in Richtung Lyon, nach (a Gallic reference to oaks) on the Rhône right bank Nordwesten in Richtung Westgallien und nach Britannia. contrary to the classical consensus, which put it at Yenne Sie passt außerdem zum Rhone-Übergang einer auf der (a probable hydronym) on the left one. Peutinger-Tafel abgebildeten Route, welche Aoste (Au- gustum) und Genf miteinander verbindet. The author is grateful to Dr. Jean-Louis Paillet and Prof. Manuel Durán Fuentes for much advice, the Notes 1 This passage was independently identified by C. Gauchon of documentation provided on Roman bridge architecture EDYTEM (Chambéry). and their ongoing encouragement. The Compagnie Na- 2 The author’s drawing of a wooden arch is based on the Dobreta and Sublicius bridges known by the Trajan column and coins, and kind tionale du Rhône must also be thanked for the considerable advice from Prof. Y. Weinand (EPF Lausanne). help it has provided for this research. 3 Brissaud 2010.

Zusammenfassung Bibliography . Artru 2006: P. Artru, Nouveaux éléments sur la voie romaine du col Eine römische Rhone-Brücke bei Pierre-Châtel, Saint-Michel et Lavisco, Le Bugey 93, 2006, 3–20. Frankreich . Artru 2011: P. Artru, Le pont de Pierre-Châtel, in: G. Barruol – J. L. Fiches – P. Garmy (eds.), Actes du colloque du Pont-du-Gard, Les ponts routiers en Gaule romaine, octobre 2008, suppl. Revue In der Schlucht Pierre-Châtel, 65 km östlich von Lyon, Archéologique de Narbonnaise, 2011 forthcoming. . Bravard – Provansal 2011: J.-P. Bravard – M. Provansal, Le entdeckte man Reste einer römischen Brücke über die franchissement du Rhône antique, in: G. Barruol – J. L. Fiches – P. Rhone. Der Fluss ist hier zu tief, um einen Pfeiler zu er- Garmy (eds.), Actes du colloque du Pont-du-Gard, Les ponts routiers en Gaule romaine, octobre 2008, suppl. Revue Archéologique de richten. Er wurde von einem einzigen Bogen mit einer Narbonnaise, 2011 forthcoming. Weite von 40–45 m überspannt. Die 114 m lange Brücke . Brissaud 2011: L. Brissaud with contr. of J.-L. Prisset, Les ponts de Vienna, in: G. Barruol – J. L. Fiches – P. Garmy (eds.), Actes lag 43 m über dem heutigen Niedrigwasserstand. Der Zu- du colloque du Pont-du-Gard, Les ponts routiers en Gaule romaine, gang am linken Ufer folgte einer natürlichen Felskante. octobre 2008, suppl. Revue Archéologique de Narbonnaise, 2011 Eine 12 m breite künstliche Aushöhlung repräsentiert den forthcoming. . Durán 2005: M. Durán Fuentes, La construccion de puentes Ankerpunkt eines ersten Bogens, welcher die Passage ei- romanos en (Santiago de Compostela 2005). ner anderen, unterhalb gelegenen Straße ermöglichte. Ein . O’Connor 1993: C. O’Connor, Roman bridges (Cambridge 1993). . Paillet 2005: J.-L. Paillet, Réflexions sur la construction du Pont du steiler Graben am rechten Ufer wird als Fundament eines Gard, Gallia 62, 2005, 49–68.

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