Built in 1495, this triumphal arch dedicated to Charles VIII is a fusion of decorative and defensive features. Its name either comes from that of an old Bordeaux family or from the "cailloux" (meaning "pebbles") that the River Garonne deposited nearby, which were used as ballast on board ships. Inside, there is an exhibition on the history of the building. On the top floor, enjoy a view over the Garonne and the Pont de Pierre.