Assos, Ephesus, Miletus, Nicaea, Pergamum, Priene, Sardis, and Aphrodisias. From the mid-5th century onwards, urbanism was affected negatively and began to decline, while the rural areas reached unprecedented levels of prosperity in the region. Historians and scholars continue to debate the cause of the urban decline in Byzantine Anatolia between the 6th and 7th centuries, variously attributing it to the Plague of Justinian (541), the Byzantine–Sasanian War (602–628), and the Arab invasion of the Levant (634–638). Medieval Period In the 10 years following the Battle of Manzikert in 1071, the Seljuk Turks from Central Asia migrated over large areas of Anatolia, with particular concentrations around the northwestern rim. The Turkish language and the Islamic religion were gradually introduced as a result of the Seljuk conquest, and this period marks the start of Anatolia's slow transition from predominantly Christian and Greek-speaking, to predominantly Muslim and Turkish-speaking (although ethnic groups such as Armenians, Greeks, and Assyrians remained numerous and retained Christianity and their native languages). In the following century, the Byzantines managed to reassert their control in western and northern Anatolia. Control of Anatolia was then split between the Byzantine Empire and the Seljuk Sultanate of Rûm, with the Byzantine holdings gradually being reduced. In 1255, the Mongols swept through eastern and central Anatolia, and would remain until 1335. The Ilkhanate garrison was stationed near Ankara. After the decline of the Ilkhanate from 1335 to 1353, the Mongol Empire's legacy in the region was the Uyghur Eretna Dynasty that was overthrown by Kadi Burhan al-Din in 1381. By the end of the 14th century, most of Anatolia was controlled by various Anatolian beyliks. Smyrna fell in 1330, and the last Byzantine stronghold in Anatolia, Philadelphia, fell in 1390. The Turkmen Beyliks were under the control of the Mongols, at least nominally, through declining Seljuk sultans. The Beyliks did not mint coins in the names of their own leaders while they remained under the suzerainty of the Mongol Ilkhanids. The Osmanli ruler Osman I was the first Turkish ruler who minted coins in his own name in 1320s; they bear the legend "Minted by Osman son of Ertugrul". Since the minting of coins was a prerogative accorded in Islamic practice only to a sovereign, it can be considered that the Osmanli, or Ottoman Turks, had become formally independent from the Mongol Khans. Ottoman Empire Among the Turkish leaders, the Ottomans emerged as great