Just west of Housesteads Roman Fort is Milecastle 37  (grid reference NY78506869). 

The milecastle has been excavated several times over the years in 1853, 1907 and 1933. The remains have been partly reconstructed and consolidated and are now in the care of English Heritage. The wall has a maximum height of 2.2 meters internally. The milecastle has a short axis, with a Type I gateway. The milecastle contains the remains of a small barrack block in the east half, which survives to 1.0 meter high.

During the excavations a re-used corner of a Hadrianic dedication slab was found in 1853, and two altars inscribed to Cocidius and Jupiter were found near the milecastle. Excavations in 1988-9 showed three periods of the north gate, having been built, blocked, then partly demolished.

Each milecartle alomg the wall has 2 associated turrets. The turrets associated with Milecastle 37 are known as Turret 37A and Turret 37B. Turret 37A, also known as Rapishaw Gap (grid reference NY78056861), was located by exploratory excavation in 1911. The turret appears to have been demolished in the Roman period. There are no visible remains of the milecastle but aerial photographs show the outline on earthworks. Turret 37B, Hotbank Crag, (grid reference NY77586847) was also located by exploratory excavation in 1911.The site is indicated by a stone-studded earthen platform.

Source Wikipedia