Plans were probably first made to construct the castle in 1284, but this was delayed due to lack of funds and work only began in 1295 following the Madog ap Llywelyn uprising.

In March 1592, the Welsh Roman Catholic priest and martyr William Davies was imprisoned in the castle, and was eventually hanged, drawn and quartered there on 27 July 1593.

[1] Following the outbreak of the English Civil War in 1642, the castle was held by forces loyal to Charles I, holding out until 1646 when it surrendered to the Parliamentary armies.

[7] Edward suppressed the rebellion over the winter and once Anglesey was reoccupied in April 1295 he immediately began to progress the delayed plans to fortify the area.

[7] The chosen site was called Beaumaris, meaning "fair marsh", whose name derives from the Norman-French Beau Mareys, and in Latin the castle was termed de Bello Marisco.

[12] This consumed around £270 a week in wages and the project rapidly fell into arrears, forcing officials to issue leather tokens instead of paying the workforce with normal coinage.

[15] The following spring, James explained to his employers some of the difficulties and the high costs involved: In case you should wonder where so much money could go in a week, we would have you know that we have needed – and shall continue to need 400 masons, both cutters and layers, together with 2,000 less skilled workmen, 100 carts, 60 wagons and 30 boats bringing stone and sea coal; 200 quarrymen; 30 smiths; and carpenters for putting in the joists and floor boards and other necessary jobs.

[17] The halt was primarily the result of Edward's new wars in Scotland, which had begun to consume his attention and financial resources, but it left the castle only partially complete: the inner walls and towers were only a fraction of their proper height and the north and north-west sides lacked outer defences altogether.

Beaumaris Castle was a strategic location in the war, as it controlled part of the route between the king's bases in Ireland and his operations in England.

[24] Thomas Bulkeley, whose family had been involved in the management of the castle for several centuries, held Beaumaris for the king and may have spent around £3,000 improving its defences.

[24] After the war many castles were slighted, damaged to put them beyond military use, but Parliament was concerned about the threat of a royalist invasion from Scotland and Beaumaris was spared.

[24] When Charles II returned to the throne in 1660 and restored the Bulkeley family as castle constables, Beaumaris appears to have been stripped of its valuable lead and remaining resources, including the roofs.

[29][nb 3] By then the castles of North Wales had become attractive locations for visiting painters and travellers, who considered the ivy-clad ruins romantic.

Although not as popular as other sites in the region, Beaumaris formed part of this trend and was visited by the future Queen Victoria in 1832 for an Eisteddfod festival and it was painted by J. M. W. Turner in 1835.

[24] In 1925 Sir Richard Williams-Bulkeley, 12th Baronet retained the freehold and placed the castle into the care of the Commissioners of Works, who then carried out a large scale restoration programme, stripping back the vegetation, digging out the moat and repairing the stonework.

[33] In the 21st century Beaumaris Castle is managed by Cadw, the Welsh Assembly Government's agency for historic monuments, as a tourist attraction, with 75,000 visitors during the 2007–08 financial year.

[36] Historian Arnold Taylor described Beaumaris as Britain's "most perfect example of symmetrical concentric planning" and for many years the castle was regarded as the pinnacle of military engineering during Edward I's reign.

[38] Nonetheless, the castle is praised by UNESCO as a "unique artistic achievement" for the way in which it combines "characteristic 13th century double-wall structures with a central plan" and for the beauty of its "proportions and masonry".

[42] The dock was protected by a wall later named the Gunners Walk and a firing platform that may have housed a trebuchet siege engine during the medieval period.