English: Caer Gybi Roman Fort was a small Roman fortlet at Holyhead (Welsh: Caer Gybi) in Wales. The original Roman name is unknown. The fort only has three walls; the fourth side fronted the sea. In the 6th Century, Saint Cybi is supposed to have founded a monastery here. The Church of St Cybi (13th century, with later extensions and additions) stands within the fort today.