In the
medieval kingdom of Gwynedd, Llanfaes functioned as the royal
demesne () and seat of local governance for the
commote of
Dindaethwy in
cantref Rhosyr King Cynan Dindaethwy maintained his
royal court () in the town around the turn of the 9th century, but he was killed amid a protracted struggle against a rival named
Hywel. Following Cynan's death, there was a major
Battle of Llanmaes () recorded in all the
Welsh annals. Various sources conjecture that the battle marked an invasion by
Mercians,
Wessaxons, or
Vikings, but the original sources simply do not record the combatants. A wooden fortress – square with a round tower at each corner – was constructed at the site by the Normans
Hugh the Wolf of
Chester and
Hugh the Red of
Shrewsbury during their
1098 invasion. During the
Battle of Anglesey Sound between the Two Hughs and
King Magnus Barefoot of
Norway, Magnus was said to have personally shot Hugh the Red through the eye with an arrow before discovering whom he was fighting and withdrawing back to the north. Llanmaes was still (or again) a
maerdref during the 12th and 13th centuries, when its royal estates encompassed 780 acres. A stream powered a mill there and it was the northernmost ferry across the
Menai Strait separating Anglesey from the mainland. The town also had a leper colony to its north. It also held two annual fairs and maintained a herring fishery. before being removed along with the monastery's other furnishings to
St. Mary's and St. Nicholas's in Beaumaris. The fortress first established by the Normans was held during the
English Civil War by Sir Thomas Cheadle on behalf of the Parliament, but was taken from him by Col. John Robinson in 1645 or '46. ==Notable people==