The city that gave its name to the see was not far from Pelusium and close to the sandhills known to Greek geographers as the Casium Mountain (Κασιον Ορος, Kasion Oros), today Ras Kouroun, El-Katieh, or El-Kas. Its ruins are at Mahemdiah.
Only one bishop is known, Lampetius, present at the Council of Ephesus in 431. Saint Cyril of Alexandria sent him, together with Hermogenes, Bishop of Rhinocorua, to Rome, where both were present at the consecration of Pope Sixtus III. Many letters of Isidore of Pelusium are addressed to him.