Castell Aberlleiniog is a Norman motte and bailey fortress built around 1088 by Hugh d'Avranches, 1st Earl of Chester, strategically positioned on the Isle of Anglesey near Llangoed. Located on private land between Beaumaris and the Menai Strait, the castle overlooks the waterway opposite the Norman castle at Abergwyngregyn. In 1094, it was besieged and captured by Gruffudd ap Cynan, with 124 Norman defenders killed in the battle, after which Anglesey remained under Welsh control. The castle's sole surviving example of a motte and bailey on Anglesey was later used by the Home Guard during World War II and owned by Penmon Priory from the 13th century until Henry VIII's suppression of the monasteries.
