Sardis or Sardes was an ancient city at the location of modern Sart (Sartmahmut before 19 October 2005), near Salihli, in Turkey's Manisa Province.

Sardis was the capital of the ancient kingdom of Lydia, one of the important cities of the Persian Empire, the seat of a Seleucid Satrap, the seat of a proconsul under the Roman Empire, and the metropolis of the province Lydia in later Roman and Byzantine times. As one of the seven churches of Asia, it was addressed by the author of the Book of Revelation in the New Testament, in terms which seem to imply that its church members did not finish what they started, that they were about image and not substance. Its importance was due first to its military strength, secondly to its situation on an important highway leading from the interior to the Aegean coast, and thirdly to its commanding the wide and fertile plain of the Hermus.

Although a mountain range limited communication with areas in the S, Sardis commanded the E-W trade route. Its commercial activity and trade, the great fertility of surrounding land, and the manufacture of woolen cloth and carpets contributed much toward making Sardis wealthy and important. At one time Sardis may have had a population of about 50,000 persons.

In the sixth century B.C.E., Cyrus the Great defeated the last Lydian king, Croesus, and for over 200 years thereafter Sardis served as the capital for the western part of the Persian Empire. In 334 B.C.E. the city surrendered without resistance to Alexander the Great. Later it came under the rule of Pergamum and then Rome. A great earthquake nearly leveled Sardis in 17 C.E., but the city was rebuilt with generous aid from Rome.

The Jewish historian Josephus indicates that in the first century B.C.E. there was a large Jewish community in Sardis. By the latter part of the first century C.E., the Christian congregation that had been established at Sardis needed to "wake up" spiritually. However, there were also persons associated with this congregation who had not 'defiled their outer garments.'

Prominent ruins at the ancient site of Sardis include those of the temple of the Ephesian Artemis (or Cybele), a Roman theater and stadium, and an ancient synagogue.