Caer y Twr

Caer y Twr (meaning 'fort of the pile/heap'[1]) is an Iron Age hillfort atop the summit of the Holyhead Mountain in Anglesey, Wales.

The hillfort, which is situated among rocky outcrops, is ideally placed for defence and likely served as a watchtower and possibly as a signal tower.

Some have speculated that it was built to alert a small fort in the modern town of Holyhead in the case of raiders coming in from the Irish Sea, while others have suggested that it may have been a lighthouse.

The hillfort is now mostly rubble, but its walls can still be made out, including a large stone rampart on the north and east sides which reaches 3 metres at points.

The footings of a tower were discovered when the site was excavated; its stones are believed to date from the 2nd to the 4th centuries.