Milecastle 42 is on a steep south-facing slope, 10 metres south of Cawfield Crags, and looks over Hole Gap to the west.

[1] The 1847–48 excavation uncovered part of a dedication slab indicating that the milecastle had been built by the Legio II Augusta.

Turret 42A (Burn Head) (grid reference NY713666) has not been located as its remains have been destroyed by quarrying.

[2] Turret 42B (Great Chesters) (grid reference NY70846682) was located by exploratory excavation in 1912.

Cawfields Picnic Area car park is on the line of the Hadrian's Wall Path, between the two sites.