The history of Caernarfon Castle

Before Edward I: Roman fort and Norman castle

Caernarfon's strategic value long predates the current castle. Half a mile away sits Segontium, a Roman fort built around AD 77 to garrison the Menai Strait region — a deliberate link to imperial power that Edward I would later echo in his own building. In the late 11th century, following the Norman invasion of Wales, Hugh d'Avranches, Earl of Chester, raised a timber motte-and-bailey castle on roughly the site of today's stone fortress. That earlier castle changed hands repeatedly: the Welsh recaptured Gwynedd in 1115 and held the site for over 150 years, including through the reign of Llywelyn ap Gruffudd ("Llywelyn the Last"), the final independent Prince of Wales.

The conquest of Wales, 1282–83

War broke out between England and Wales in March 1282. Llywelyn ap Gruffudd was killed in December that year; his brother Dafydd ap Gruffydd fought on until his last stronghold, Dolbadarn Castle near Llanberis, fell in May 1283. With Wales effectively conquered, Edward I moved immediately to fortify his gains, beginning new castles at Harlech and Caernarfon within weeks of Dolbadarn's capture.

Building the castle, 1283–1330

Construction began in the summer of 1283 under Master James of St George, a military architect from Savoy who by then had already worked on Edward's castles at Conwy and elsewhere, and who was formally appointed Master of the King's Works in Wales around 1285. Work was deliberately concentrated on the castle's southern side first, since the new town walls — built simultaneously — already protected the north.

The whole project, covering the castle, the walled town, and a quay on the River Seiont, took some 47 years and cost around £20,000–£25,000 — an enormous sum for the period, paid for out of English royal revenue at a time when the average labourer earned a few pence a day. The castle's walls enclose roughly 4.2 acres, with a perimeter of about 734 metres (2,408 ft).

The 1294 revolt

The castle was tested almost immediately. In 1294, a Welsh uprising led by Madog ap Llywelyn briefly captured the still-unfinished town and castle, causing significant damage to the incomplete northern defences. The revolt was suppressed, and the episode prompted a renewed, more urgent focus on strengthening the castle's northern wall and the imposing King's Gate.

Why it looks the way it does

Caernarfon is deliberately different from Edward's other Welsh castles. Where Conwy and Harlech are more conventionally military, Caernarfon's polygonal towers and bands of different-coloured stone — grey-brown local sandstone banded with paler limestone — are widely understood to be a conscious echo of the Theodosian Walls of Constantinople. The symbolism reached further still: medieval Welsh legend told of Macsen Wledig (the Roman emperor Magnus Maximus), who dreamed of a great fort at the mouth of a river, "the fairest that man ever saw." By building here, and in this style, Edward was asserting a lineage of imperial authority stretching back to Rome — a message aimed as much at his newly conquered Welsh subjects as at any military threat.

Later centuries & decline

Work effectively stopped around 1330, and the castle was never completed — several of the planned interior buildings within its walls were never built, which is part of why the interior today feels more open than a typical medieval castle. Caernarfon saw further action during the Wars of the Roses and was garrisoned for the Crown during the English Civil War in the 1640s, successfully withstanding three sieges by Parliamentarian forces. By the 18th and 19th centuries it had fallen into picturesque ruin, becoming a subject for Romantic painters before restoration work began in earnest in the Victorian period.

The princes of Wales & the 1911 and 1969 investitures

Edward of Caernarfon, born at the castle in 1284, was created the first English Prince of Wales in 1301 and later reigned as Edward II. Centuries later, the ceremonial investiture of the monarch's heir at Caernarfon was revived for Edward VIII in 1911, and again for Charles — later King Charles III — on 1 July 1969, watched by an estimated 500 million people worldwide.

Read the full story of the 1969 investiture →

UNESCO World Heritage status

In 1986, Caernarfon Castle and its town walls were inscribed by UNESCO as part of the "Castles and Town Walls of King Edward in Gwynedd" World Heritage Site, alongside Conwy, Harlech and Beaumaris castles. UNESCO recognises the group as an outstanding example of medieval military architecture, prized for how completely the castles and their associated town defences survive.

The castle today

Today Caernarfon Castle is cared for by Cadw, the Welsh Government's historic environment service — not the National Trust or English Heritage, a point of confusion common enough that we've given it its own page. Two of its towers house the Royal Welch Fusiliers Museum, and visitors can climb the Eagle Tower and walk long stretches of the wall walk for views over the town and the Menai Strait toward Anglesey.