Book excerpt: In the last years of his reign Henry VIII needed a radically modern system of defence to protect England and its new Church. Anticipating a foreign onslaught from Catholic Europe after his split from Rome, Henry energetically began construction of more than 20 stone forts to protect England's major ports and estuaries. Aided by excellent illustrations, Peter Harrington explores the departure from artillery-vulnerable medieval castle designs, to the low, sturdy stone fortresses inspired by European ideas. He explains the scientific care taken to select sites for these castles, and the transition from medieval to modern in this last surge of English castle construction.