Aberystwyth Castle is located in Aberystwyth, Ceredigion, Wales. The castle, now in ruins, is mere yards away from the sea. Though Aberystwyth was begun in 1277, the area has hosted other castles before it, the earliest being a fortress dating to the Iron Age.

Aberystwyth was built as a diamond-shaped concentric fortress, with gatehouses at each point. Its walls-within-walls defenses allowed its guards to fire down from different heights, helping to avoid friendly fire. Beyond its guardtowers, the castle had two gatehouses, a barbican and a tall tower in the castle's inner ward. Today the castle rubble only hints at its past, its imposing structure destroyed by warring and its proximity to the sea. Historical accounts suggest that the castle had already begun to decay by 1343 due to wind and water erosion.

It is open to the public, and includes a park built in recent years by local town leaders.

History
The first true castle built at Aberystwyth was erected about a mile south of the current castle site by Gilbert de Clare circa 1110, and was variously called Castell Tan-y-castell, Aberrheidol Castle and Old Aberystwyth, among others.

This timber castle (later reinforced with stone) changed hands repeatedly as the Normans warred with the native Welsh, who were firmly ensconced in this area of Wales. The castle first fell to Owain Gwynedd in 1136. The castle's ownership switched at least three more times before being captured by Llywelyn the Great in 1221. Scholars believe that Llywelyn probably razed the castle and rebuilt another one in its place. It is not mentioned again until Edward I erected what is now known as Aberystwyth Castle a mile north of this site.

Aberystwyth was built, along with Flint Castle, Rhuddlan Castle and Builth Castle, by King Edward I as part of his campaign against the Welsh. Aberystwyth, started in 1277, was a particularly taxing job. It still was not completed by 1282 when the Welsh briefly captured and burned it. Construction was finally completed in 1289 at great expense to the crown.

By 1307 the castle was thriving enough that people had made their homes next to its walls, and the town was decreed Llanbadarn Gaerog (Fortified Llanbadarn). But the town was commonly referred to by the castle's name, as is the case today.

The castle changed hands several times as the Welsh and English warred throughout Wales, including by Owain Glyndŵr, who took possession of the castle in 1404. The English soon after recaptured the castle, but by 1408, peace having been struck, the castle began to fall into disrepair. Still, in 1637 Aberystwyth was designated as a royal mint by Charles I. The mint struck silver coins. This association became the castle's downfall, as the mint's operator, who had been made wealthy by his job, raised a regiment of Royalist soldiers during the English Civil War. This made Aberystwyth a target of Oliver Cromwell, who scourged the castle in 1649.