 The fort is designed as a defensible battery , rather than a defensive strongpoint . The faces of the fort join to form a half @-@ moon shape or lunette . The guns ' primary role was to defend Port Adelaide and the Semaphore anchorage rather than the fort itself , and the design reflects this . It was intended to be supported by field artillery , cavalry and infantry for self @-@ defence and to repel landings . While the fort retains its original form , the ditch and glacis ( embankment ) have been modified and are largely non @-@ <unk> in some areas . Ground levels have been changed to accommodate paths and a caravan park , and the original western fence no longer exists . 
