Celetrum or Keletron (Ancient Greek: Κέλετρον) was a town of Orestis region in Upper Macedonia (today: Western Macedonia, Greece), situated on a peninsula which is surrounded by the waters of a lake, and has only a single entrance over a narrow isthmus which connects it with the continent.

[4] The position is so remarkable that there is no difficulty in identifying it with the modern town of Kastoria.

The peninsula is nearly four miles (6 km) in circumference, and the outer point is not far from the centre of the lake.

The later fortification of Kastoria consists only of a wall across the western extremity of the isthmus, which was built in the time of the Byzantine Empire, and has a wet ditch, making the peninsula an island.

The ruins of a parallel wall flanked with round towers, which in Byzantine times crossed the peninsula from shore to shore, excluding all the east part of it, in the 19th century divided the Greek and Turkish quarters of the town.