Dorylaion (modern Eskişehir) is a city of northwestern Phrygia on a strategic road junction controlling passage from Constantinople to the interior of Asia Minor. A major military post, Dorylaion was frequently mentioned after 741, when it was base of the revolt of Artabasdos. It was a bastion of the Opsikion theme and an Aplekton; Arab raids often reached it in the 8th-10th centuries. According to Ibn Khordadbeh, Dorylaion was noted for its plains, where imperial pack animals were raised, and for its hot springs. After the Turks captured it around 1080, Dorylaion lay in ruins in a no-man's land frequently occupied by nomadic Turkish tribes until Manuel I took the region in 1175, drove out the nomads, and built a new fortress for defense of the frontier. Soon after the battle of Myriokephalon, however, the city fell to the Seljuks. Dorylaion was a bishopric of Phrygia Salutaris, under Synada. Remains of the fortifications, which surrounded the medieval hilltop town, have entirely disappeared; they indicated two periods of construction, perhaps of the 7th-8th and 12th century.
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Oxford Dictionary of Byzantium