Caernarfon is the traditional county town of the traditional county of Caernarfonshire and was a county corporate in its own right. The town is best known for its great stone castle, built by Edward I of England and consequently sometimes seen as a symbol of English domination. Edward's architect, James of St. George, modelled the castle on the walls of Constantinople - Edward being devoted to the Crusader cause. On higher ground on the outskirts of the town are the remains of an earlier occupation, the Segontium Roman Fort.

The population of Caernarfon is largely Welsh-speaking (92% of the population reported some level of Welsh ability in the 2001 census) and the town is nowadays a rallying-point for the Welsh Nationalist cause. In 1911, David Lloyd George, then Member of Parliament for the borough, conceived the idea of holding the investiture of the new Prince of Wales at Caernarfon Castle, believing that this would help pacify nationalist opinion whilst arousing a more British patriotic feeling. The ceremony took place on July 13, with the royal family paying a rare visit to the principality, and the future King Edward VIII was duly invested.