The Porte Guillaume is the western gate of St-Valéry's medieval circuit — a pair of squat round towers flanking a stone archway, named for William the Conqueror and traditionally identified as the gate through which his army marched out toward the waiting fleet in 1066. Whether or not the story is true, the gate has stood here since at least the thirteenth century, with patched repairs from every period between then and now.
Walk through and you step from the wider lower town into the cobbled lanes of the upper quarter. The view back from inside the arch, framing the chalk cliff and the houses climbing the slope, is one of the most photographed in town.