Timeline

Heritage classified

Origin and history

The Saint-Michel bridges and the so-called chastre bridges (or carriageways) are medieval monuments located at the southern exit of Blois, partly on the town of Saint-Gervais-la-Forêt (Loir-et-Cher). These works, mentioned in 1202 for the Saint-Michel bridges and 1343 for the chastres, allowed to cross the flood bed of the Cosson and the Loire. Their structure combines raised dikes and arches, adapted to the frequent floods of the region. They were part of the old Roman route linking Chartres to Bourges, reused until the 18th century.

The origin of the term "cartrains" is uncertain: it could be a deformation of chastres (cuts), evoking their segmented shape. The Saint-Michel bridges, located on an ancient road, today preserve only vestiges of medieval piles, while the chastised bridges, still practical, underwent partial reconstructions in the 17th and 18th centuries. Their heterogeneous masonry testifies to these successive changes to resist the variations of the river.

Ranked historic monuments in 2006, these bridges illustrate ancient wetland management techniques. Their route follows the old rural road of the carriageway bridges, crossing Saint-Gervais-la-Forêt, Vineuil and Blois. Although modified over the centuries, they remain the last examples of this type of layout in the Loire Valley, mixing Gallo-Roman heritage and medieval adaptations.

Historical sources highlight their key role in regional exchanges, particularly between Chartres and Bourges. Their partial abandonment in the 19th century, after the construction of new carriageways, preserved rare archaeological elements. Today, their property is shared between public and private domains, with protected remains such as the bases of the Saint-Michel Bridge batteries.

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