Criccieth Castle a distant relation of Llywelyn ap Gruffudd, began an uprising against English rule that spread quickly through Wales. Several English-held towns were razed and Criccieth (along with Harlech Castle and Aberystwyth Castle) were besieged that winter. Its residents survived until spring when the castle was resupplied. In the 14th century the castle had a notable Welsh constable called Hywel ap Gruffydd, known as Howell the Axe, who fought for Edward III at the Battle of Poitiers in 1356. The castle was used as a prison until 1404 when Welsh forces captured the castle during the rebellion of Owain Glyndŵr. The
Richard Beauchamp, 13th Earl of Warwick military action in Wales, defending against a Welsh rebellion led by Owain Glyndŵr. On 22 July 1403, the day after the Battle of Shrewsbury, he was made a Knight of the Garter. In the summer of 1404, he rode into what is today Monmouthshire at the head of a force. Warwick engaged Welsh forces at the Battle of Mynydd Cwmdu, near Tretower Castle a few miles northwest of Crickhowell – nearly capturing Owain Glyndwr himself, taking Owain's banner, forcing the Welsh to flee. They were chased down the valley of the River Usk where they regrouped and turned the tables