In each case the defences provided by the inhabitants consist of earthen banks, the materials of which have been dug from the fosses or ditches which surround their outer face. An earthen bank and fosse, thrown across the neck of land between the promontory and the plateau beyond, convert the extremity of the promontory into a fortified enclosure. Well-known examples of such fortresses are the three camps, one on the east and two on the west side of the river, which guarded the valley of the Avon at Clifton. The labour necessary for the construction of these was naturally far less than that which went to the making of the great contour fortresses, of which so many splendid examples remain in Somerset, Wiltshire, Dorset, and in the chalk districts generally. In these cases, the whole area, or at any rate the greater part of it, stood in need of entrenchment. There are points at which the slope is so precipitous that the bank and ditch were dispensed with, or, as in part of Cissbury camp near Worthing, only a single bank or ditch was necessary.[1] Also, the steeper the ground, the less was the labour required in constructing the entrenchments. But these positions often took the form of enclosures surrounded by double or triple lines of defence, often of stupendous size. For the greater part of its extent, the _vallum_ or bank of the oval camp of Cissbury is double, and along the outer edge of the encircling fosse is a formidable counterscarp or parapet. Poundbury, which lies on the high ground west of Dorchester, has a single bank and ditch on its east and south sides. On the west side the bank is doubled; but the north side, where the hill falls almost perpendicularly to the Frome, was left without artificial defence. The superb fortress of Maiden Castle (2), which crowns an isolated hill, 432 feet high, south of Dorchester, shows a bewildering complication of plan. The oval central space is ringed by a number of banks and ditches, which varies from three on the north side to as many as eight about the western entrance. [Illustration: Maiden Castle; plan]