Lake Copais, also spelled Kopais or Kopaida (Ancient Greek: Κωπαΐς; Greek: Κωπαΐδα), was a lake in the centre of Boeotia, Greece, west of Thebes. It was first drained in the Bronze Age, and drained again in the late 19th century. It is now flat dry land and is still known as Kopaida. A one-time island in the lake was modified in ancient times into a megalithic citadel, now called Gla.