Beaumaris is known as the greatest castle that was never built. Conceived to stand alongside Caernarfon, Conwy and Harlech as outposts of English power in Wales, work was started by Edward I in 1295.

Estimates suggest that there are at least 1 million castles on the planet today, with many of them being reduced to ruins. Wales is home to about 600 of those castles, with about 100 of them standing ...