'Caer Gybi' was a small
fortlet in the
Roman province of
Britannia. 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.

St Cybi's Church at Holyhead
The fort is one of
Europe's only three-walled
Roman forts. The fourth side fronted the sea and probably the site of a
quay. Its date is unknown, but it is generally thought to be part of a late
4th century scheme, associated with
Segontium, which was set up to defend the west coast against
Irish sea-raiders. The Romans also built a watch tower, within Mynydd y Twr, on the top of
Holyhead Mountain which was almost certainly used as the fort's look-out point. Both were probably abandoned around
393 when the troops were probably sent to respond to the revolt of
Eugenius of Gaul. 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.
References
★
Roman & Early Medieval Wales, , Christopher J, Arnold, Sutton Publishing, ,