Milecastle 19 (Matfen Piers) was a milecastle of the Roman Hadrian's Wall. Sited just to the east of the hamlet of Matfen Piers, the milecastle is today covered by the B6318 Military Road. The milecastle is notable for the discovery of an altar by Eric Birley in the 1930s. An inscription on the altar is one of the few dedications to a mother goddess found in Roman Britain, and was made by members of the First Cohort of Varduli from northern Spain. The presence of the Vardulians at this milecastle has led to debate amongst archaeologists over the origins of troops used to garrison the wall. A smaller altar was found at one of the two associated turrets.

A milecastle was a small fort (fortlet), a rectangular fortification built during the period of the Roman Empire. They were placed at intervals of approximately one Roman mile along several major frontiers, for example Hadrian's Wall in Great Britain, hence the name.