Milecastle 17 (Welton/Whittledean) was a milecastle of the Roman Hadrian's Wall. The milecastle is located near to the Whittle Dene reservoirs and is visible as a platform in the ground. Just 174m west of the milecastle is a distinct change in wall construction, indicating that it may have formed a boundary between different legions. The existence of the milecastle has been known since at least 1732 and excavations have produced numerous finds and evidence of post-Roman occupation. The associated turrets both lie beneath the B3618 Military Road. A stone found near the milecastle is the only known written record of the name of Gaius Julius Marcus, a Roman Governor of Britain whose name has been erased from other inscriptions possibly because he fell out of favour with Emperor Caracalla.