Old Burrow and Martinhoe are situated on the rocky North Devon coast, 1100 and 800 ft. high respectively above the seas of the Bristol Channel (PL. LIIa) , on either side of the small seaside town of Lynmouth. Both sites command an extensive view of the South Wales coast, 17 to 20 miles away (FIG. 4), but owing to an intervening hill, the Foreland, they are not intervisible. Inland the outlook is limited to the northern slopes of Exmoor, which rises to 1600 ft. some 6 to 7 miles away. The coastal tract in which they are situated was sparsely inhabited by friendly Iron Age peoples, the Dumnonii, living in small hillforts and isolated from the main body of the tribe in South Devon and Cornwall.

The Roman earthworks are practically identical (FIGS. I and 3); they consist of an inner rectilinear enclosure, 90 ft. square defended by a rampart and two ditches, set within a rounded outer enclosure, some 300 ft. in diameter and with a single rampart and ditch. At Martinhoe the outer enclosure ends on the cliffs, which form its northern side.

The entrance to the inner fartlet in both cases is on the seaward side; to the outer on the opposite landward side, so that all comers would be obliged to make a half-circuit between the two lines of defences under fire. In effect the device resembles that at the Claudian fort at Hod Hill in Dorset, where the defences were also designed to trap attackers within the range of missiles—spears or ballista bolts.