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Segontium Roman Site

A Scheduled Monument in Caernarfon, Gwynedd

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Latitude: 53.1374 / 53°8'14"N

Longitude: -4.2658 / 4°15'56"W

OS Eastings: 248528

OS Northings: 362420

OS Grid: SH485624

Mapcode National: GBR 5J.688M

Mapcode Global: WH43F.FDXP

Entry Name: Segontium Roman Site

Scheduled Date: 4 November 1976

Source: Cadw

Source ID: 3611

Cadw Legacy ID: CN006

Schedule Class: Defence

Category: Fort

Period: Roman

County: Gwynedd

Community: Caernarfon

Built-Up Area: Caernarfon

Traditional County: Caernarfonshire


This monument comprises the remains of a Roman auxiliary fort dating to AD 77. Overlooking the Menai Strait, the fort was named after the nearby river Seiont (Saint). Segontium was part of a network of other forts linked by a strategic road system and formed part of the Roman imperial arrangement for controlling the newly conquered Welsh tribes. Throughout the Roman period Segontium was the military and administrative centre of north-west Wales.

Segontium was set out in a typical Roman fort layout. It is shaped like a playing card, with defences of earth and timber, symmetrically placed gates and streets, and a fairly standardized arrangement of timber-framed buildings. From AD 140 – though somewhat earlier in the case of several buildings – the fort was subject to prolonged piecemeal rebuilding of both its defences and internal buildings in stone.

Visible remains include barracks, buildings with underfloor heating (hypocaust), storehouses, a bathhouse and the praetorium – the garrison commander’s house. The third- to fourth-century principia (headquarters building) is situated at the centre of the fort. Beyond this is a colonnaded court with a well and the basilica (cross hall) which comprised the ceremonial heart of the fort where the unit could assemble and the commanding officer could issue orders and hold court martials. At the rear of this building is the shrine (aedes) where statues of the god Jupiter and the emperor were kept alongside the regimental standards. In the third century a vaulted strongroom (sacellum) was built within the basilica to hold the garrison’s pay-chest and savings. The flanking rooms were offices.

Archaeological excavations have shown that the fort was designed to accommodate a regiment of auxiliary infantry up to 1000 strong. The name of only one of the units that garrisoned the fort is known: the First Cohort of Sunici, a 500-strong infantry regiment originally recruited from Germany. Coins recovered from excavation show that Segontium was garrisoned until about AD 394. This extraordinarily long occupation, unique in Wales, is explicable by the fort’s strategic position controlling access to the fertile and mineral-rich lands of Anglesey.

This monument is of national importance for its potential to enhance our knowledge of the Roman conquest of Wales. The scheduled area comprises the remains described and an area around them within which related evidence may be expected to survive.

Source: Cadw

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