At the call of Pope Urban II, William took up the cross of the First Crusade in the army of Raymond IV of Toulouse. He served notably at the capture of the small Syrian village of Ma'arrat al-Numan in 1098. After the fall of Jerusalem in 1099, William remained in the Holy Land for a while. He remained at the side of Godfrey de Bouillon and accompanied him to the siege of Antioch in December 1097. He did not return to Montpellier until 1103, bringing with him a relic of Saint Cleopas.