 The scar or cliff and hence the milecastle are named after an ancient tenement called The Harrows which stood nearby.The tenement is shown on William Howard's 1603 map of the Barony of Gilsland and on an estate map of The Shaws commissioned by John Carrick around 1800.Harrows Scar measures 19.8 metres east to west by 22.9 metres north to south and no contemporary internal buildings are now visible.