Onnum (Halton Chesters) was an auxiliary fort on Hadrian's Wall, situated where Dere Street crosses the Wall about 6 km west of Corbridge. Built in stone c. AD 122–125 as part of the original Wall scheme, it covered roughly 1.7 ha and was occupied, with periods of refurbishment and partial abandonment, into the late 4th century. The fort straddled the Wall in its primary phase, projecting north of it, and was later extended westward in the Severan period.
Source: Pleiades — A Community-Built Gazetteer and Graph of Ancient Places. View the Pleiades record →
Its position controlling the junction of Dere Street—the principal north–south military road into Scotland—with the Wall made it strategically important for monitoring traffic through this key crossing point. Garrison evidence includes the ala Sabiniana, a cavalry regiment attested in the 3rd century by the Notitia Dignitatum and inscriptions, reflecting the site's role as a mounted patrol base.
The fort plan is well known from aerial photography and from excavations by John Gillam and others in the 1930s–60s, which revealed the headquarters building, commanding officer's house with a bath suite, granaries, and the unusual western extension. Geophysical survey has also mapped an extensive vicus and field system south of the Wall, though much of the interior remains unexcavated and the site is not displayed to the public.
Onnum (Halton Chesters) was an auxiliary fort on Hadrian's Wall, situated where Dere Street crosses the Wall about 6 km west of Corbridge. It is recorded in the Pleiades gazetteer of ancient places as a fort site from the Roman period in Britain.
Onnum is classified as a Roman fort — a military site in the Pleiades ancient world gazetteer. Roman Britain's archaeology encompasses thousands of sites ranging from legionary fortresses and marching camps to villas, temples and towns.
Several Roman sites lie within a short distance, including Turret 21A (Red House) (0.2 km), Turret 21B (Fence Burn) (0.3 km), Milecastle 21 (Down Hill) (0.7 km). Aubrey Research maps over 2,200 Roman sites across Britain, drawn from the Pleiades ancient world gazetteer.
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