This small cruciform compartment, called a logette, housed the relic that has now disappeared: a piece of wood from the True Cross. It has been replaced by an engraved silver cross. The Wasnes-au-Bac cross is part of a large production of reliquaries designed to house the relics of the True Cross brought back mainly after the sack of Constantinople in 1204 during the 4th Crusade (1202-1204).