The town of Alasehir, ancient Philadelphia, is a district of Manisa province in Turkey. Apart from being an ancient city in Anatolia, it was one of the seven churches written to by St. John in the Book of Revelation.

The original city was founded by Attalos Philadelphos II, one of the kings of Pergamum, in the 2nd century BC. The last king of Pergamum bequeathed his kingdom, including Philadelphia, to his Roman allies when he died in 133 BC. The city, which maintained its importance during the Pergamon rule, became one of the most important centers of the Romans in Anatolia and developed further due to its strategic location. Philadelphia was called as Little Athens during the Roman period due to the number of temples and festivals held here. The city suffered badly in an earthquake in AD 17, but it was rebuilt. The citizens accepted Christianity around 40 AD, which boosted its importance from a religious perspective being one of the seven churches in Asia Minor. In the 14th century, Philadelphia was made the metropolis of Lydia by the Greek Orthodox patriarch of Constantinople.

During the Byzantine period the city was an important producer of leather goods and red-dyed silk. Philadelphia was also an important military base of Byzantium and therefore was exposed to many attacks. However, strong walls surrounding the city saved its inhabitants from invaders. The city has changed hands between the Byzantines and the Turks throughout history; the Seljuks took it in 1074, then the Crusaders, and finally the Ottomans in 1390. Philadelphia remained a major Christian center until the population exchange between Greece and Turkey of 1923.

Today, there are few historical artifacts left in Philadelphia from the Byzantine period due to many earthquakes in the past. The medieval artifacts that can be identified in the city are quite remarkable; ruins of Basilica of St. John, Byzantine city walls, a theater and a temple dating back to the Roman period. During the excavations in the theater, a large part of the stage building and a small part of the seats were unearthed. One of the most magnificent monuments of the city is the Church of St. John, built in the 6th century, of which only three pillars are currently preserved.