The fort lay at the eastern end of Hadrian's Wall (in Wallsend) near the banks of the River Tyne, forming the eastern-most portion of the wall. It was in use as a garrison for approximately 300 years, almost up to 400AD.
Today, Segedunum is the most thoroughly excavated fort along Hadrian's Wall.
The Roman Wall was originally built to end at Pons Aelius (Newcastle). Work began in Pons Aelius in 122AD and proceeded towards the west. Subsequently, it was decided that the Wall should be extended further east, probably to protect the river crossing at Pons Aelius. In about 127AD, work was begun on a further four-mile section of the Wall east from the fort of Pons Aelius, passing through present-day Byker and ending at the new fort of Segedunum. The new section of wall was narrower than the sections previously built, being 7ft 6in on a foundation of 8ft. Unlike the existing wall, the extension had no vallum behind it.
The fort measured 453ft from north to south and 393ft from east to west, covering and area of 4.1 acres. A wide ditch and an earth embankment surrounded the fort on all sides. It had four double gates with the east, west and north gates opening outside the wall and only the south gate opening within the Wall. The Wall joined to the west wall of the fort just south of the west gate. From the southeast angle of the fort, a 6ft 6in wide wall ran down to the riverbank and extended at least as far as the low water level.
There is evidence that there was an extensive vicus, or village surrounding the fort, including the area to the north of the wall.
The original garrison of Segedunum is unknown, but in the second century the Second Cohort of Nervians was stationed there. In the third and fourth centuries the part-mounted Fourth Cohort of the Lingones occupied the fort. Both units were 600 strong. 120 cavalry and 480 infantry
Sometime round about 400AD the fort was abandoned. For centuries the area remained as open farmland, but in the eighteenth century, collieries were sunk near the fort and the area gradually became a populous pit village. Eventually, in 1884, the whole fort disappeared under terraced housing.
In 1929 some excavations were carried out which recorded the outline of the fort. The local authority marked out this outline in white paving stones. In the 1970s the terraced houses covering the site were demolished.
A section of Hadrian's Wall was excavated and a reconstruction built in the early 1990s. The Segedunum project began in January 1997 with a series of excavations in and around the Fort, as well as the construction of the Bath House and the conversion of former Swan Hunter shipyard buildings to house the new museum. Segedunum Roman Fort, Baths & Museum opened to the public in June 2000.
The site of the fort now contains the excavated remains of the buildings' foundation of the original fort, as well as a reconstructed Roman military bathhouse based on excavated examples at Vindolanda and Chesters forts. A museum contains items of interest that were found when the site was excavated and a large observation tower overlooks the site. A portion of the original wall is visible across the street from the museum, and a reconstruction of what the whole wall might have looked like when new. This eastern portion of Hadrian's Wall was erected atop the Whin Sill, a geological formation which offers natural topographic defence with respect to invaders or immigrants from the north.
The name Segedunum is known from the Notitia Dignitatum of the 4th century, but there is no consensus on its meaning. The various conjectures include "derived from the Celtic for 'powerful' or 'victorious'", "derived from the [Celtic] words sego ('strength') and dunum ('fortified place')", "Romano-British Segedunum 'Strong-fort'", and "Celtic sechdun or 'dry hill'".
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