Constructed as part of a wider project to create the walled town of Conwy, the combined defences cost around £15,000, a massive sum for the period.

It withstood the siege of Madog ap Llywelyn in the winter of 1294–95, acted as a temporary haven for Richard II in 1399 and was held for several months by forces loyal to Owain Glyndŵr in 1401.

In the aftermath, the castle was partially slighted by Parliament to prevent it being used in any further revolt, and was finally completely ruined in 1665 when its remaining iron and lead was stripped and sold off.

Divided into an Inner and an Outer Ward, it is defended by eight large towers and two barbicans, with a postern gate leading down to the river, allowing the castle to be resupplied from the sea.

It retains the earliest surviving stone machicolations in Britain and what historian Jeremy Ashbee has described as the "best preserved suite of medieval private royal chambers in England and Wales".

Built on a rocky outcrop, with an apsidal tower, it is a classic, native, Welsh build and stands out from the rest of the town walls, due to the presence of four window openings.

The location also controlled an important crossing point over the River Conwy between the coastal and inland areas of North Wales, that Deganwy Castle for many years had defended.

[3] The kings of England and the Welsh princes had vied for control of the region since the 1070s and the conflict had resumed during the 13th century, leading to Edward I intervening in North Wales for the second time during his reign in 1282.

[6] Edward's plan was a colonial enterprise and placing the new town and walls on top of such a high-status native Welsh site was in part a symbolic act to demonstrate English power.

[14] Chronicler Walter of Guisborough suggested that given the austere conditions Edward refused to drink his own private supply of wine, and instead had it shared out amongst the garrison.

[16] Conwy Castle was not well maintained during the early 14th century and by 1321 a survey reported it was poorly equipped, with limited stores and suffering from leaking roofs and rotten timbers.

[17] Sir John Weston, his chamberlain, conducted repairs, building new stone support arches for the great hall and other parts of the castle.

[19] In April 1401, on Good Friday, Rhys ap Tudur and his brother Gwilym, cousins of Owain Glyndŵr, undertook a surprise attack on Conwy Castle.

[25] The Archbishop defected to Parliament, the town of Conwy fell in August 1646 and in November General Thomas Mytton finally took the castle itself after a substantial siege.

[28] The work was completed under the supervision of Edward Conway's overseer William Milward, despite opposition from the leading citizens of Conwy, and turned the castle into a total ruin.

[29] By the end of the 18th century, the ruins were considered picturesque and sublime, attracting visitors and artists, and paintings of the castle were made by Thomas Girtin, Moses Griffith, Julius Caesar Ibbetson, Paul Sandby and J. M. W.

[30] Already protected as a scheduled monument, in 1986 it was also declared part of the World Heritage Site of the "Castles and Town Walls of King Edward in Gwynedd".

[35] In December 2023, Condé Nast voted the castle as the most stunning in Europe, beating the likes of Eilean Donan in Scotland, and Kylemore Abbey in Ireland.

[37] The local stone was not of sufficient quality to be used for carving details such as windows, however, and accordingly sandstone was brought in from the Creuddyn peninsula, Chester and the Wirral.

[40] Although now somewhat decayed, the battlements originally sported triple finial designs and featured a sequence of square holes running along the outside of the walls.

[42] When first built, the barbican was reached over a drawbridge and a masonry ramp that came up sharply from the town below; the modern path cuts east along the outside of the walls.

[60] These include window styles, the type of crenellation used on the towers and positioning of putlog holes, and are usually ascribed to the influence of the Savoy architect Master James.

[60] Notably the three pinnacled merlons are a feature seen at the Savoyard Castello San Giorio di Susa which had been visited by Edward on his way back from crusade in 1273.