1. A Stone Wall with a ditch on its northern side.
2. A series of forts, mile-castles and Wall turrets, connected by roads.
3. An earthwork known as "The Vallum," consisting of a deep central ditch and two (frequently three and sometimes four) earthern mounds, running always to the south of the Wall and its fortifications.
Excavations and inscriptions have now pretty well established the order and the period in which the different parts were constructed, and it appears to have been as follows:
1. Agricola built a series of forts (including Corbridge and Carlisle) across the isthmus, about 79 A.D., with a road, afterwards known as the Stanegate, connecting them.
2. Hadrian first built a new line of forts a short distance to the north of the Stanegate line.
Fig. 1.—Section showing the relative positions of the Stone Wall, the Vallum and the Military Way.