Coordinates: 55°01′14″N 2°06′35″W / 55.020461°N 2.109670°W / 55.020461; -2.109670
Milecastle 26 (Planetrees) was a milecastle of the Roman Hadrian's Wall. Its position is slightly to the south of, but mostly covered by the B6318 Military Road., and it is located around 700 metres (0.43 mi) east of the B6318 Military Road's junction with the A6079. No visible traces exist currently. The dimensions are the same as Milecastles 23, 24, and 25.
Measuring 15.24 metres (50.0 ft) across, Milecastle 26 was a long-axis milecastle with unknown gateway type. Such milecastles were thought to have been constructed by the Legio VI Victrix who were based in Eboracum (York).
A causeway over the wall ditch (not necessarily primary) may have existed at the location of the milecastle.
The curtain wall is broad at this point, though changes to narrow gauge between here and Turret 26A, at an extant section of the curtain wall known as Planetrees. Also, in 1956, two iron wedges for splitting stones (260 millimetres (10 in) and 260 millimetres (10 in) long) were discovered in the rubble and mortar core behind the north facing stones of the wall in a trench cut beside the farm.