Turret 21B (Fence Burn) was one of the standard interval watchtowers on Hadrian's Wall, positioned between Milecastles 21 (Down Hill) and 22 (Errington Hill Head) in the central sector east of Portgate. Like other turrets on the Wall, it was constructed in the AD 122–130s under Hadrian, originally built into the broad Wall in stone, and would have functioned as a two-storey observation and signalling post manned by a small detachment from the nearest fort, probably Halton Chesters (Onnum). The Wall turrets in this sector were generally abandoned or demolished during the later 2nd or 3rd century as the garrison strategy shifted toward concentration in the forts.
Source: Pleiades — A Community-Built Gazetteer and Graph of Ancient Places. View the Pleiades record →
Its significance lies in its role as part of the integrated surveillance and communication system of the Wall in the rolling country east of the North Tyne, providing line-of-sight observation across the Fence Burn valley and signalling links to flanking turrets and milecastles. It is not individually distinguished in the literature on the Wall.
Very little is recorded specifically for Turret 21B; unlike well-known excavated turrets such as 26B (Brunton) or 29B (Black Carts), it has not been the subject of significant published excavation, and its remains are largely subsurface. Its position is established by the regular Roman spacing along the Wall rather than by extensive structural investigation.
Turret 21B (Fence Burn) was one of the standard interval watchtowers on Hadrian's Wall, positioned between Milecastles 21 (Down Hill) and 22 (Errington Hill Head) in the central sector east of Portgate. It is recorded in the Pleiades gazetteer of ancient places as a watch tower site from the Roman period in Britain.
Turret 21B (Fence Burn) is classified as a Roman watch tower — 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 Onnum (0.3 km), Turret 21A (Red House) (0.4 km), Milecastle 22 (Portgate) (0.5 km). Aubrey Research maps over 2,200 Roman sites across Britain, drawn from the Pleiades ancient world gazetteer.
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