From Wikipedia, the free encyclopedia
Jump to: navigation, search
Porolissum-porta-praetoria-icon.png Segontium
Segontium Roman Fort - - 1287434.jpg
Segontium is located in Gwynedd
Red pog.svg Segontium shown within Gwynedd
Founded 77 or 78 AD
Abandoned 4th century AD
Place in the Roman world
Province Britannia
— Stone structure —
Built 2nd century AD
— Wood and earth structure —
Built 1st century AD
Coordinates 53°08′14″N 4°15′57″W / 53.1373°N 4.2659°W / 53.1373; -4.2659
Town Caernarfon
County Gwynedd
Country Wales
UK-OSNG reference SH485624
Site notes
Controlled by Cadw
Media related to Segontium at Wikimedia Commons

Segontium is a Roman fort located 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 from the River Seiont. But it may also be connected to the Segontiaci, a British tribe mentioned by Julius Caesar.

Although the Roman occupation of Britain ended around 400 AD, the legacy of the Segontium survived. The medieval name of the town Caernarfon is derived from "Caer yn ar-Fon" which means "Fort in (the land) opposite Mon".



Segontium was founded by Agricola in 77 or 78 AD 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 AD. 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 120 AD there had been a reduction in the military numbers at the fort.[citation needed]

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 394 AD.

Later periods[edit]

In the 11th century the Normans built a motte near the site of the River Seiont. This was succeeded by Caernarfon Castle, which was built by Edward I after he had conquered Wales in the 13th century.

Present day[edit]

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.

Mythology and fiction[edit]

Segontium is referenced in the prose of the Mabinogion, a collection of early medieval Welsh poetry first collated in the 1350s. In Breuddwyd Macsen Wledig ("The dream of Macsen Wledig") - one of the Four Independent Tales - Macsen (who is identified with the Roman usurper, Magnus Maximus) dreams of a beautiful woman who turns out to be at "the fort at the mouth of the Seiont".

Wallace Breem's novel Eagle in the Snow begins and ends in post-Roman Segontium, and references the temple of Mithras.

The fort also features in Mary Stewart's Merlin trilogy, specifically in The Crystal Cave and The Hollow Hills.


See also[edit]

  • Caer Gybi at Holyhead — established in the 4th century to support Segontium against Irish raiders.


  • Frances Lynch (1995) A guide to ancient and historic Wales: Gwynedd (HMSO)
  • R.E. Mortimer Wheeler (1924) Segontium and the Roman occupation of Wales (Honourable Society of Cymmrodorion)

External links[edit]