Milecastle 21


Milecastle 21 was a milecastle of the Roman Hadrian's Wall. The site was identified by measurement only, as the milecastle's remains have been totally removed. This is probably due to extensive quarrying at the site, which now lies under pasture.

Construction

No details of the Milecastle's construction have been identified.

Excavations and investigations

Each milecastle on Hadrian's Wall had two associated turret structures. These turrets were positioned approximately one-third and two-thirds of a Roman mile to the west of the Milecastle, and would probably have been manned by part of the milecastle's garrison. The turrets associated with Milecastle 21 are known as Turret 21A and Turret 21B.

Turret 21A

Turret 21A is probably located to the east of the east wall of Onnum, though some doubt has been expressed by an English Heritage field investigation. Its remains lie under the modern road.
Location on Ordnance Survey 1:25 000 map:

Turret 21B

Turret 21B is probably located partly beneath the military road, though the exact location has been speculated due to the presence of a small mound along with dark soil and pottery discovered in 1930.
Location on Ordnance Survey 1:25 000 map:

Monument Records