Caernarfon Castle was originally founded around 1090AD, when the Norman lord Hugh d'Avranches built a series of fortifications in north Wales in an attempt to secure his recently conquered territories. This early castle would have been a motte and bailey construction, typical of other early Norman strongholds.

In 1115AD, the Welsh recaptured Gwynedd, along with Caernarfon Castle. They held it until 1282AD, when Edward I began his second campaign in Wales. The king led the northern segment of a three-pronged attack, completing the conquest of Gwynedd by 1283AD. Edward immediately began to consolidate his control of Wales by undertaking to build a series of new castles at Harlech, Conwy and Caernarfon. Caernarfon Castle was built on the site of the earlier fortification, and incorporated the early Norman motte into its layout.

James of Saint George was the continental master-mason and architect employed by Edward to deliver these impressive fortresses. He had already worked on other Welsh castles, and his military engineering skills were crucial in creating Edward's "Iron Ring" around Wales. At Caernarfon, James created an entire fortified outpost, which would serve as the administrative centre of Gwynedd. Town walls were added to enclose the castle, and a new quay was built to enable supplies to arrive by sea. Work continued through 1283AD-1294AD, with stone being quarried as far away as Anglesey, and timber being brought in from the area around Liverpool.

During the summer of 1283AD, the king and his wife took up residence in Caernarfon Castle for a month, living in temporary timber structures while work on the stone fortification was still underway. The following year, they returned to the castle, and the queen gave birth there to Edward II. It is likely that this was intentionally arranged for its symbolism.

In 1294AD, Caernarfon was captured by the Madog ap Llywelyn, Prince of Wales, during a Welsh uprising. By 1295AD however, the English had recaptured it. Extensive damage had been done to the town walls, and these were repaired at great expense. Work continued on the castle, and was ongoing until around 1330AD. Expenditure on the project was enormous, giving some idea of the importance of this site to the English crown. No major alterations or additions took place after this time.

When Owain Glyndŵr rose up against the English crown, Caernarfon Castle presented a natural target for his army. Between 1403AD-1404AD, it was placed under siege by Welsh rebels. However, the defending forces were able to hold out with a garrison of only 30 men. The castle continued to serve as an administrative centre for North Wales for the next 150 years, with no record of it seeing further military action.

In 1485AD, Henry VII succeeded to the throne of England. Henry was of Welsh descent on his father's side, and was born in Pembroke Castle. Welsh troops had fought on his side at the Battle of Bosworth. Accordingly, his strong ties with Wales (or at least the perception of those ties) was a factor in reducing tensions between Wales and the English throne. This reduced the strategic importance of castles such as Caernarfon, and they fell into a state of neglect.

Caernarfon Castle saw a final period of action during the English Civil War, when it was still strong enough to withstand three sieges, before finally surrendering to parliamentary forces in 1646AD. In 1660AD, Caernarfon's slighting was ordered, with the intention of putting it beyond military use. However, it appears that this work never began, allowing the castle to survive to the present day in remarkable condition. Despite this, maintanance of the castle ceased, and it fell into decay until the Victorians undertook restorative works in the 19th Century.

Caernarfon Castle's unique heritage led to its use in 1911AD for the investiture of the Prince of Wales. This tradition was continued in 1969AD, when Prince Charles was invested there. Unusually, the castle (despite being in the care of CADW) has remained the property of the crown since the time it was built. In 1986AD, it was granted World Heritage Site status by UNESCO.

The prestige of Caernarfon Castle was apparently very much in the minds of those who originally built it. Most historians now agree that the symbolism of its location (near the Roman fort of Segontium, linked with the legend of Magnus Maximus, the rebel Roman emperor of Wales), combined with is unusual design (bands of coloured stone and angular towers, invoking an image of Constantinople, capital of the Byzantine Roman Empire) were deliberately intended to lend Caernarfon an air of imperial grandeur. According to legend, Maximus dreamed of a castle that was "the fairest that man ever saw", located within a city at the mouth of a river, in a mountainous country and opposite an island. It seems likely that Edward was very intentionally inviting the conclusion that Caernarfon was the manifestation of this legend.

Visiting Caernarfon today, it is easy to appreciate the powerful impression that the castle must have made on the medieval mind. It is a truly magnificent structure, still dominating the town above which it stands. Its walls are immense, punctuated by nine huge towers and two daunting gatehouses. Although the walls and towers are essentially intact, none of the interior buildings have survived.

Exploring Caernarfon Castle involves navigating the honeycomb of tunnels and passages that run throughout the curtain wall. High vantage points give an impressive view of the surrounding terrain, along with an impression of how completely the medieval street plan survives within the old town walls. Overall, this is a truly unique and impressive site, and the jewel in the crown of Welsh castles.