Beaumaris Castle (derived from the Norman "fair marsh") was built as part of Edward I's campaign to subjugate Wales. Work began in 1295AD, following the uprising of Madog ap Llywelyn. It was constructed on a virgin site of flat marshland, with no earlier fortification to inhibit the design. Building work was finished in 1330AD, although the towers, gatehouses and defences were never fully completed. This was partly the result of the death of Edward I in 1307AD (along with his architect Master James of St George in 1309AD), but additionally, the focus of the English crown had shifted towards the border with Scotland. Wales was largely conquered, and the position of Beaumaris Castle meant that it was of limited strategic value.

Beaumaris Castle has been hailed as a masterpiece of Norman military design. It features two concentric defensive walls, with a moated outer ward guarded by twelve towers and two gatehouses, overlooked by an inner ward with two large gatehouses and six substantial towers. The castle was also designed to allow re-supply via a sea-gate, furthering its defensive potential.

Despite its formidable design, Beaumaris Castle fell to the Welsh rebellion of Owain Glyndŵr in 1403AD. This was possibly due to its incomplete nature, or possibly due to an inadequate garrison. From this, it is reasonable to infer that the original defensive blueprint was never fully tested. Beaumaris was recaptured by the English in 1405AD.

By 1538AD, a survey described the castle as "ruinous and decaying". Nevertheless, in 1642AD it was garrisoned by forces loyal to Charles I. They surrendered to a Parliamentarian army in 1646AD, without resistance.

Beaumaris Castle subsequently fell out of the history books, and is not heard of again until 1807AD, when Viscount Thomas Bulkeley bought the ruins and incorporated it into the park surrounding his residence at Baron Hill (itself now a ruin, tucked away in woods to the west of Beaumaris Castle).

Today, Beaumaris Castle is in the care of CADW, and represents one of the best preserved examples of late-medieval military architecture in Britain. Despite its unfinished state, the ruins provide a very clear impression of the overall design, offering a clear understanding of the architect's vision.

Beaumaris Castle was the last of Edward I's great coastal castles, and it is in some ways fitting that it lies in a quieter corner of Wales, slightly awkward to reach and neglected by the majority of tourists. Stunning views across the Menai Straight to the mountains of north Wales enhance the setting, making this ruin a truly special place to visit.