In which castle was King Charles III invested as Prince of Wales in 1969?

King Charles III was invested as Prince of Wales in 1969 at Caernarfon Castle, which holds significant historical and cultural importance. This event was symbolically important, marking the investiture of the heir to the British throne in a location that has been associated with the Welsh and the British crown for centuries.

Caernarfon Castle was specifically chosen for this occasion due to its imposing stature and its deep-rooted connection to Welsh identity, as it was originally constructed by Edward I in the late 13th century during his campaign to conquer Wales. The invested ceremony was designed to reflect the close ties between the monarchy and Wales, emphasizing the role of the Prince of Wales as a representative figure for this region.

Other castles listed like Cardiff Castle, Conwy Castle, and Beaumaris Castle, while they hold their own historical significance, were not the site of this particular ceremonial event for Charles's investiture. Caernarfon's historical context and its strategic importance within Wales solidify it as the correct answer to this question.