Castercliff is an Iron Age multivallate hillfort situated close to the towns of Nelson and Colne in Lancashire, Northern England.

It is located on a hilltop overlooking the valley system of the River Calder and its tributaries, on the western edge of the South Pennines.

On the upper part of the hill, triple rubble ramparts up to 1.5 metres (4 ft 11 in) high, separated by ditches of similar depth, surround the site on all sides except the north.

The inner rampart may have been timber-laced and revetted with stone and enclosed an oval area measuring approximately 115 by 76 metres (377 by 249 ft).

[1] The summit of the hill is 280 metres (920 ft) above sea level and the surrounding ground falls rapidly on all sides except the south east.