Qasr Libya or Qasr Lebia (, lit. 'Lebia Castle', Lebia/Libya being a corruption of the ancient name Olbia) is a small town in northern Libya about 66 km northwest of Bayda. In ancient times, it was a Roman / Byzantine town called Olbia and Theodorias, the ruins of which were excavated in the 1950s. The town contains a museum with fifty Byzantine mosaics. It is on the cross-roads between the eastwards Marj–Bayda main road, and the southwards Qasr Libya–Marawa road.