The bridge of the valley (listed as a historical monument), in granite, is built in the 15th century, probably by Richard d'Etampes the father of Duke Francis II to connect the suburbs of the Trinity and Saint Anthony to the closed town of Clisson.
The particularity of this bridge lies in the presence of its 6 waterways, arches of unequal dimensions.
• The waterway to the left bank at the foot of the castle was once crossed by a drawbridge, the “Porte de la Vallée”.
• Three waterways, a central waterway, touching the right and left banks (after the drawbridge was destroyed) were equipped with wooden bridges in the Middle Ages. These 3 wooden bridges were as much passive defense and could be destroyed in the event of an assault from the suburbs. These bridges were replaced by stone vaults in the 19th century.
 This bridge has 5 granite spurs that aim to divert piles, the strong current during floods, tree trunks and sometimes ice drifting. Many times submerged since the Middle Ages, this bridge resists however thanks to the spurs. In addition, spurs are a refuge for pedestrians when crossing horse-drawn carriages.
 The cross on the 3rd spur was once on Notre Dame Square. On the 4th spur, there remains a granite pedestal on the site of a cross that marked the boundaries between the parishes of Notre Dame and the Trinity.