Dascylium, Dascyleium, or Daskyleion (Ancient Greek: Δασκύλιον, Δασκυλεῖον), also known as Dascylus, was a town in Anatolia some 30 kilometres (19 mi) inland from the coast of the Propontis, at modern Ergili, Turkey. Its site was rediscovered in 1952 and has since been excavated.
Excavations have shown that the site was inhabited in the Bronze Age. Phrygians settled there before 750 BC. It came under the control of Lydia. It was then said to be named after Dascylus, the father of Gyges.
Pharnabazus was satrap of Darius III there, until Alexander the Great appointed Calas, who was replaced by Arrhidaeus in the Treaty of Triparadisus. According to Strabo, Hellespontine Phrygia and Phrygia Epictetus comprised Lesser Phrygia (Mysia). Others geographers arranged it differently.
When Alexander of Macedon invaded Asia in 334 BC, the first of the major battles by which he overthrew the Achaemenid Empire was fought at the Granicus river on his way to Dascylium from Abydos on the coast.
Dascylium appears as a Christian bishopric in the mid-7th-century Notitia Episcopatuum of Pseudo-Epiphanius. It was a suffragan of the metropolitan see of Nicomedia, capital of the Roman province of Bithynia.
The first bishop of Dascylium whose name appears in an extant document is Ioannes, who took part in the Third Council of Constantinople in 680 and in the Trullan Council of 692. The priest Basilius acted as representative of an unnamed bishop of the see at the Second Council of Nicaea in 787. Georgius was at the Council of Constantinople (869) and Germanus at the Photian Council of Constantinople (879).