Coordinates: 55°00′54″N 2°02′25″W / 55.014932°N 2.040394°W / 55.014932; -2.040394
Milecastle 23 (Stanley) was a milecastle of the Roman Hadrian's Wall. Its remains exist as a low, grass covered platform with traces of an external ditch (as Milecastle 25). It is located to the south of the B6318 Military Road around 1.5 kilometres (0.93 mi) west of its junction with the A68.
Milecastle 23 was a long-axis milecastle. The gateway type is unknown, though long-axis milecastles were thought to have been constructed by the Legio VI Victrix who were based in Eboracum (York).
The milecastle measured 15.24 metres (50.0 ft) across, and had broad east and west walls (the curtain wall at this point was also broad gauge). The width of the south wall is unknown.
The ditch at the point corresponding to the milecastle's north gate undergoes a slight change in profile in the bottom. Also, there is an 8 metres (26 ft) gap in the upcast mound at the same point. These features indicate the existence of a causeway, later removed. There was also eveidence of an equivalent causeway across the vallum, and gaps in the vallum mounds (also removed).