The Bridge of Gran Arvou spans the Rû Prévôt irrigation canal, and includes a large corridor covered by flagstones.
The Grand Arvou is an arch bridge, with a span of 68.5 m and an elevation of 13,60 m between the arch's top and the ground; the distance between the roof and the base of the arch is 10,5 m. The bridge is built in mortar and small incoherent stones, with partial plastering. The plan is irregular, with a general trapezoidal shape, but without the main parallel side; the walls's thickness varies from 50 to 55 cm. The roof is covered by flagstones, which helped it resist to the centuries.
In the late 13th-early 14th century, there was a series of programs aiming to improve the irrigation level in Aosta Valley, due to increased demand of animal husbandry. One of this was the construction of canal, the Rû Prévôt, by will of Henry of Quart, provost (hence the name) of the Aosta Cathedral. This included also the couple of bridge-aqueducts which are now visible.
The income of the canal exploitation was later acquired by the Dukes (later Kings) of Savoy. In the 20th century, the canal was mostly channeled into pipes.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.