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 77 are known as Turret 77A (grid reference NY255611) and Turret 77B (grid reference NY251612). The exact locations of the turrets have not been found.[2]