Book excerpt: Throughout history, Cambridgeshire (including Huntingdon and Peterborough) has figured in many of the conflicts which have shaped our nation. Doomed Roman legionaries marched from Longthorpe to defeat by Boudicca's Iceni; Saxons and Danes fought over the edges of the Danelaw; the Normans came this way to crush Hereward's Fenland resistance; in the Civil War it provided the defended frontier between Parliamentarian and Royalist; in Napoleonic times French prisoners of war were incarcerated here; and in the twentieth century its flat expanses were home to numerous airfields and missile bases. This book describes the function and purpose of these defensive structures and reveals the evidence which many of these major events left on the ground: the earthworks of hill forts, medieval castles and moats; the masonry of later forts and strong-houses; drill halls and militia barracks; and the lines of anti-invasion defences from 1940.