St Cybi's Church, Holyhead

Caer Gybi ("Cybi's Fort") is a late Roman military enclosure on the western end of Holyhead harbour — built in the 4th century AD (probably during the reign of Magnus Maximus, c.380–388 AD) as part of the Roman coastal defence system against Irish raiders. The fort is one of the best-preserved examples of Roman military architecture in Wales, with three of its original four walls still standing to near-original height and incorporating characteristically Roman features including external projecting towers. After the Roman withdrawal from Britain in the early 5th century, the fort was repurposed: according to Welsh tradition, King Maelgwn Gwynedd (died 547 AD) granted the fort to St Cybi as the site for his monastic community. The high, solid walls of the Roman enclosure provided ideal protection and structure for a monastic settlement — the walls were already built and robust — and St Cybi's community established itself within them, creating the unique situation that persists today: a functioning Christian church and churchyard enclosed within Roman fort walls.

St Cybi was a 6th-century Celtic saint, probably of Cornish or South Welsh origin, who became the patron saint of Holyhead (the Welsh name Caergybi — "Cybi's Fort" — preserves his name as directly as any Welsh place name preserves a saint's identity). Cybi is associated with founding monastic communities in several locations in Wales and possibly in Ireland. His principal foundation was at the Roman fort on Holy Island — the site that became Caergybi/Holyhead — where he established a monastic community under the patronage of Maelgwn Gwynedd. St Cybi is celebrated on 8 November in the Church of Wales calendar. He is said to have been a friend and contemporary of St Seiriol (the patron of Penmon Priory on the opposite end of Anglesey, after whom Puffin Island/Ynys Seiriol is named) — the two saints are associated in a famous Welsh tradition as the "bright saint" (Cybi, whose church faces east, walking east into the rising sun to visit Seiriol) and the "dark saint" (Seiriol, walking west into the setting sun to visit Cybi).

The Roman fort walls of Caer Gybi are immediately accessible in the centre of Holyhead — they form the boundary of the church enclosure and are visible and walkable from the street around the outside. The walls are built in the characteristic Roman style: large, roughly squared blocks of local stone with courses of tile for structural bonding, external projecting towers (polygonal bastions) at intervals, and gates on the east and west sides. Three of the four original walls survive to significant height (up to 3–4 metres in places); the northern wall, facing the sea, has been more damaged. The quality and extent of the Roman masonry is impressive — and unexpected in the middle of a busy port town. The walls can be viewed from the outside at any time; entry to the churchyard (enclosed within the walls) gives a different perspective on the enclosed space and the relationship between Roman fortification and medieval church.

The current church building at St Cybi's dates primarily from the 13th–16th centuries, though the site has been in continuous ecclesiastical use since at least the 6th century. The church is a substantial cruciform building (nave, chancel, north and south transepts) — larger than most rural Welsh churches of similar age, reflecting Holyhead's importance as a port and the status of the St Cybi foundation. The interior has been restored but retains medieval features including a 16th-century chapel (the Stanley Chapel, with monuments to the Stanley family — earls of Derby — who held estates on Anglesey). The nave has a 14th-century character. The church is still in regular use as a parish church. The churchyard within the Roman walls contains old grave markers and ancient yew trees. The combination of working medieval parish church, historic monuments, and Roman enclosure walls makes a visit to St Cybi's a genuinely unusual experience.

St Cybi's Church and Caer Gybi are the oldest surviving structures in Holyhead — a town that has been continuously occupied since at least the Roman period and whose modern identity is dominated by the ferry port (the busiest Irish Sea crossing, with regular services to Dublin). The church and Roman fort are a few metres from the port entrance, sitting between the modern ferry terminal and the town centre. The Holyhead Maritime Museum (0.3 miles, in the former 1858 lifeboat station) covers the port's 2,000-year maritime history from the Roman period to the present. The RNLI lifeboat station at the pier is one of the most active in Wales. South Stack RSPB reserve (3 miles) and Trearddur Bay (3 miles) provide the natural history counterpart to the town's built heritage. The combination of Roman fort, medieval church, Victorian maritime heritage, and wild coastal scenery within 3 miles makes Holyhead a more rewarding destination than its industrial ferry-port character might initially suggest.