Aberystwyth Castle is an Edwardian fortress that was built during the First Welsh War in the late 13th century. It was begun during Edward I's first Welsh campaign at the same time as work started at Flint, Rhuddlan and Builth Wells.

Building work started in 1277. The inner ward was built in a diamond-shaped concentric castle, with a twin D-shaped gatehouse keep with mural towers at each corner. The outer ward consisted of twin D-shaped gatehouse, a barbican, a rock-cut ditch and a large curtain wall with towers.

Marcher lord Gilbert de Clare built an earlier Motte and bailey castle a mile south of the current site in c.1110. It was called Castell Tan-y-castell, Aberrheidol Castle and Old Aberystwyth. The earth and timber castle was later reinforced with stone. The castle was captured by Owain Gwynedd in 1136: it then changed hands at least three more times before being capturedl by the Welsh prince Llywelyn the Great in 1221. Llywelyn razed this castle and built another one in its place.

Aberystwyth Castle had not yet been completed when the Welsh briefly captured and burned it in 1282. Later work was overseen by master mason James of St George. Construction ceased in 1289. The castle was subjected to a lengthy siege during the revolt of Madog ap Llywelyn in 1294-5.

By 1307 a town was thriving outside the castle walls; its Welsh name was Llanbadarn Gaerog (English: Fortified Llanbadarn). However historical accounts suggest that the castle had already begun to fall into disrepair by 1343.

During the national uprising led by Owain Glyndŵr, the Welsh took possession of the castle in 1404. But the English had recaptured the castle by 1408. In 1637 Aberystwyth Castle was designated as a Royal mint by Charles I, and produced silver shillings. The mint's operator raised a regiment of Royalist soldiers during the English Civil War. Oliver Cromwell slighted the castle in 1649.