This is a promontory fort, a type of coastal enclosure in which the natural defences of a sea cliff do most of the work. The landward side, the only approach an enemy could realistically use, was blocked by one or more earthen banks and ditches, while the sea did the rest. The result is an enclosed space that commands views across open water and drops sheer to the rocks below, the kind of place that was clearly chosen with as much tactical thought as ceremonial or practical intent.