Caer Gybi was a small fortlet in Roman Wales in the Roman province of Britannia Superior. Its name in Latin is unknown. Today it stands at the centre of Holyhead in the Welsh county of Anglesey. Holyhead is named Caergybi in Welsh, after the fort. In the 6th century, the old fort was given to Saint Cybi, who founded a monastery there. The Church of St Cybi still stands on the site today, with a small detached chapel over Cybi's grave.