Philadelphia (now know as Alaşehir) was a city of Lydia and last Byzantine possession in Asia Minor. It is one of the seven churches of the province of Asia listed in the Book of Revelations.

Philadelphia was significant in the 6th century, when the followers of Proklos called it "little Athens" because of its festivals and temples. John Lydos, however, described the suffering of his native Philadelphia under John the Cappadocian, whose agents ruthlessly extracted taxes. Philadelphia, a city of the Thrakesion theme, was occupied by the Turks after the Battle of Mantzikert in 1071, but was recovered by the Byzantine in 1098. It became capital of the theme by the mid-12th century, and was a major bulwark of the frontier, and base for imperial expeditions to the east. The city was a center of resistance to Andronikos I in 1182 and the capital of Theodore Mankaphas. Philadelphia flourished under the Laskarids, when it was administered by a stratopedarches of Philadelphia and Thrakesion. It was a center of trade, with colonies of Venetians (attested in 1188) and Genoese (1342), and was noted for its production of leather goods and red-dyed silk. 
In the 14th century, Philadelphia, as the easternmost Byzantine city, was frequently attacked by the Turks. Rescued by the Catalan Grand Company in 1304, it was forced to pay tribute to Germiyanafter the siege of 1309/10. From 1322 to 1324 it endured a long siege by Germiyan and Aydin, the account of which reveals many details of local topography. Two bishops of that era, Theoleptos  and Makarios Chrysokephalos, played an enormous role in administering and defending the city. Philadelphia was then a Byzantine enclave surrounded by Turkish emirates, prospering through trade and its strategic location. It finally fell to Bayezid I in 1390. 
Philadelphia, which was a suffragan bishopric of Sardis, became an independent metropolis under Isaac II and metropolis of Lydia in 1369. Philadelphia owed its survival in part to its long and powerful walls, whose extensive remains appear to date to the 3rd and 12th-13th century. The city also preserves the ruins of a large domed basilica, evidently Justinianic.