Harrows Scar measures 19.8m east to west by 22.9m north and no contemporary internal buildings are now visible. It is built with narrow gauge defensive walls which are bonded with the Narrow Wall curtain of Hadrian's Wall on either side. It has Type III gateways. It lies 1458m west of Milecastle 48 and 1391m east of Milecastle 50. It was excavated in 1898, and in 1953 by I.A. Richmond, when parts of the underlying Turf Wall milecastle (49TW) were identified. The monument is currently in the care of English Heritage. It was designated as a Scheduled Monument (number:13987) on 14 July 1997.