Much has been written about the decline and fall of the feudal fortress: much less has been written about the British fortifications that were built in the age of artillery. From the early and dangerous days of gunpowder to the threat of nuclear annihilation, the state has responded to the threat of invasion or attack by building strongholds. Here, the author reveals what fortifications were built to contain insurrection in Scotland in the eighteenth century and Ireland in the twentieth century. How in 1940 Britain put its faith in the pillbox and the secret structures built for defence in the Cold War.