In 1205, following the destruction of the Byzantine Empire by the forces of the Fourth Crusade, the Crusaders under William of Champlitte and Geoffrey of Villehardouin marched south through mainland Greece and conquered the Peloponnese against sporadic local Greek resistance. The Franks then founded the Principality of Achaea, nominally a vassal of the Latin Empire, while the Venetians occupied several strategically important ports around the coast such as Navarino and Coron, which they retained into the 15th century. The Franks popularized the name "Morea" for the peninsula, which first appears as the name of a small bishopric in Elis during the 10th century. Its etymology is disputed, but it is most commonly held to be derived from the mulberry tree ("morea"), whose leaves are similar in shape to the peninsula.