Segontium Roman Fort

Caernarfon, United Kingdom

Segontium is a Roman fort on the outskirts of Caernarfon in Gwynedd, North Wales. The fort, which survived until the end of the Roman occupation of Britain, was garrisoned by Roman auxiliaries from present-day Belgium and Germany. It was the most important military base and administrative centre in this part of Britain.

The fort probably takes its name either directly from the Afon Seiont or from a pre-existing British settlement itself named for the river. 

Segontium was founded by Agricola in AD 77 or 78 after he had conquered the Ordovices in North Wales. It was the main Roman fort in the north of Roman Wales and was designed to hold about a thousand auxiliary infantry. It was connected by a Roman road to the Roman legionary base at Chester, Deva Victrix. Unlike the medieval Caernarfon Castle that was built alongside the Seiont estuary more than a thousand years later, Segontium was situated on higher ground to the east giving a good view of the Menai Straits.

The original timber defences were rebuilt in stone in the first half of the 2nd century. In the same period, a large courtyard house (with its own small bathhouse) was built within the fort. The high-status building may have been the residence of an important official who was possibly in charge of regional mineral extraction. Archaeological research shows that, by the year 120, there had been a reduction in the military numbers at the fort. An inscription on an aqueduct from the time of the Emperor Septimius Severus indicates that, by the 3rd century, Segontium was garrisoned by 500 men from the Cohors I Sunicorum, which would have originally been levied among the Sunici of Gallia Belgica. The size of the fort continued to reduce through the 3rd and 4th centuries. At this time Segontium's main role was the defence of the north Wales coast against Irish raiders and pirates. Coins found at Segontium show the fort was still occupied until at least 394.


In the 11th century, the Normans built a motte nearby, whose settlement formed the nucleus of present-day Caernarfon. Following the 13th-century Edwardian conquest, the earlier work was replaced by Caernarfon Castle.

Present day

Although the A4085 to Beddgelert cuts through the site, most of the fort's foundations are preserved. Guidebooks can be bought from other Cadw sites, including Caernarfon Castle. The remains of a civilian settlement together with a Roman temple of Mithras, the Caernarfon Mithraeum, and a cemetery have been also identified around the fort.



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Founded: 77-78 AD
Category: Prehistoric and archaeological sites in United Kingdom


3.9/5 (based on Google user reviews)

User Reviews

Dave Holland (8 months ago)
When we visited this attraction the front gate was open but the information centre was closed. No opening times were displayed. Bring your imagination when you visit as there is only one information board at the back of the information centre. (Maybe there's more information in the centre!!!) The best photo of this area is on Google maps, just so you get the size of the area in perspective. Unfortunately the road and houses were built on the site. We didn't visit the baths over the road as there's no information on how or where to get in. The locals know how to get in both sites as dogs where being walked in the fort and lads where playing football in the baths. Do you think these ruins will last another 2000 years.?
A “Itsjustme” D (17 months ago)
Really well maintained and free access if you go around the back of the small building. Just one information board hence the loss of one star, otherwise what a great place. A great place to gather pine cones too.
Evalynn B. (19 months ago)
I had a 2 weeks holiday in Wales in 2019 and wanted to visit this place on the day when I visited the castle, too. So I parked next to the castle, and after visiting that, I walked uphill on the streets to find the roman fort. I could not find any opening hours anywhere - Google map, Tripadvisor or Visit-Wales website, was not stated any hours. It was a Saturday about 1pm, and I found the place closed. Even on the gate there was not a sign showing opening times just a big padlock. Only a notice not to climb on the monument, but the gate was locked otherwise. I just walked near the fence a few minutes trying to find someone on the ground, and met on the street another disappointed visitor, so we shared our frustration about the lack of the opening times anywhere. In the meantime - which was just 2 minutes maybe - we have seen a man with his 8-10 years old son climb over the fence and go into the ground... No Comment. Maybe this was the way to get in??? Very disappointing visit, and that I walked a lot uphill to find the big nothing. At least on Google map should be stated the opening hours. Hopefully it has been changed since then, otherwise no point to visit.
CM H (2 years ago)
It's a shame that the museum was closed but you can still walk around to the back where the ruins are. Theres a lot of base bricks in the shape of where the walls of the buildings would have been so bring your imagination because NO Information is given. ?????
Mitsh'au'nuruodo (2 years ago)
Considering this is a free site to visit, this is a huge treasure of heritage, and well worth a visit. This isn't just almost two thousand years old and still very visible, but it's also incredibly important in this region's history. Even folk stories that begin dynasties from which the Princes of Wales begin their origin stories were founded here. The site's quite large, well-maintained, and there are information boards to learn from, too; but you'll be best served by reading some more about this before/after your visit - particularly concerning emperor Macsen.
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