Using this system, the various structures were numbered after the Milecastle located to the east of the object.
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.
The milecastle is notable for the discovery of an altar by Eric Birley in the 1930s.
Milecastle 66 was seen by Thomas Pennant in 1772, when he passed through Carlisle on his way to Scotland.
Coins of Tetricus I and also Valentinian I (indicating the milecastle to be one of only 10 yielding 4th century material)