Madog ap Llywelyn in the context of "Beaumaris Castle"

Caernarfon Castle (Welsh: Castell Caernarfon; Welsh pronunciation: [kastɛɬ kaɨrˈnarvɔn]) is a medieval fortress in Gwynedd, north-west Wales. The first fortification on the site was a motte-and-bailey castle built in the late 11th century, which King Edward I of England began to replace with the current stone structure in 1283. The castle and town established by Edward acted as the administrative centre of north Wales, and as a result the defences were built on a grand scale. There was a deliberate link with Caernarfon's Roman past—nearby is the Roman fort of Segontium—and the castle's walls are reminiscent of the Walls of Constantinople.

While the castle was under construction, town walls were built around Caernarfon. The work cost between £20,000 and £25,000 from the start until the work ended in 1330. Although the castle appears mostly complete from the outside, the interior buildings no longer survive and many parts of the structure were never finished. In 1294 the town and castle were sacked and captured by Madog ap Llywelyn during his rebellion against the English, but were recaptured the following year. The castle was unsuccessfully besieged during the Glyndŵr Rising of 1400–1415. When the Tudor dynasty ascended to the English throne in 1485, tensions between the Welsh and English began to diminish and castles were considered less important. As a result, Caernarfon Castle was allowed to fall into a state of disrepair.

Harlech Castle (Welsh: Castell Harlech; Welsh pronunciation: [kastɛɬ ˈharlɛχ]) in Harlech, Gwynedd, Wales, is a Grade I listed medieval fortification built onto a rocky knoll close to the Irish Sea. It was built by Edward I during his invasion of Wales between 1282 and 1289 at the relatively modest cost of £8,190. Over the next few centuries, the castle played an important part in several wars, withstanding the siege of Madog ap Llywelyn between 1294 and 1295, but falling to Prince Owain Glyndŵr in 1404. It then became Glyndŵr's residence and military headquarters for the remainder of the uprising until being recaptured by English forces in 1409. During the 15th-century Wars of the Roses, Harlech was held by the Lancastrians for seven years, before Yorkist troops forced its surrender in 1468, a siege memorialised in the song "Men of Harlech". Following the outbreak of the English Civil War in 1642, the castle was held by forces loyal to Charles I, holding out until 1647 when it became the last fortification to surrender to the Parliamentary armies. In the 21st century the ruined castle is managed by Cadw, the Welsh Government's historic environment service, as a tourist attraction.

UNESCO considers Harlech, with three others at Beaumaris, Conwy and Caernarfon, to be one of "the finest examples of late 13th century and early 14th century military architecture in Europe", and it is classed as a World Heritage Site. The fortification is built of local stone and concentric in design, featuring a massive gatehouse that probably once provided high-status accommodation for the castle constable and visiting dignitaries. The sea originally came much closer to Harlech than in modern times, and a water-gate and a long flight of steps leads down from the castle to the former shore, which allowed the castle to be resupplied by sea during sieges. In keeping with Edward's other castles in the north of Wales, the architecture of Harlech has close links to that found in the County of Savoy during the same period, an influence probably derived from the Savoy origins of the main architect, James of Saint George.