A 2017-human genetics study showed that the Peloponnesians have little admixture with populations of the Slavic homeland and are much closer to Sicilians and southern Italians. Apart from the troubled relations with the Slavs, the coastal regions of the Peloponnese suffered greatly from repeated Arab raids following the Arab capture of Crete in the 820s and the establishment of a corsair emirate there. After the island was recovered by Byzantium in 961 however, the region entered a period of renewed prosperity, where agriculture, commerce, and urban industry flourished. 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. Frankish supremacy in the peninsula, however, received a critical blow after the Battle of Pelagonia, when William II of Villehardouin was forced to cede the newly constructed fortress and palace at Mystras near ancient Sparta to a resurgent Byzantium. This Greek province (and later a semi-autonomous Despotate) staged a gradual reconquest, eventually conquering the Frankish principality by 1430. The same period was also marked by the migration and settlement of the Arvanites to Central Greece and the Peloponnese. The Ottoman Turks began raiding the Peloponnese from c. 1358, but their raids intensified only after 1387 when the energetic Evrenos Bey took control. Exploiting the quarrels between Byzantines and Franks, he plundered across the peninsula and forced both the Byzantine despots and the remaining Frankish rulers to acknowledge Ottoman suzerainty and pay tribute. This situation lasted until the Ottoman defeat at the Battle of Ankara in 1402, after which Ottoman power was for a time checked.