Caerau Hillfort

Caerau Hillfort is a large triangular multivallate Iron Age hillfort, built on a previously occupied Neolithic site, occupying the western tip of an extensive ridge-top plateau in the western suburbs of Caerau and Ely, Cardiff, Wales. It is the largest Iron Age site of its type in south Wales and also one of the largest in Great Britain. The old parish church, St Mary's, and a small ringwork, almost certainly a medieval castle site probably contemporary with the church, stand within the hillfort on the north-eastern side.

Source: Wikipedia