Wales, a small country, is littered with the relics of war – Iron Age forts, Roman ruins, medieval castles and the coastal forts of the eighteenth and nineteenth centuries. The biggest construction of fortifications in Wales took place during the reign of Edward I. They were not only built to deter an invader, but to control the frequent Welsh uprisings. The next wave of constructions occurred during the eighteenth and nineteenth centuries, when a number of forts and gun emplacements were built, mostly in South Wales, to deter a seaborne invasion. The twentieth century introduced a new mode of defence, especially during the two world wars, in the form of pillboxes, tank traps and gun emplacements. The various airfields constructed were the most visible form of defence and could be regarded as the castles of the period. This book looks at how Welsh castles protected Wales to make it what it is today.