Sam Willis looks at the history of the castle from its first appearance with the Normans in 1066 to the longest siege on English soil at Kenilworth Castle 200 years later. The castle arrived as an instrument of invasion, but soon became a weapon with which unruly barons challenged the crown. Tingtagel Castle, the place King Arthur is said to have been conceived, is also on the itinerary. It remains one of the most evocative of castles to this day, drawing visitors from around the world with its tales of myth and legend.

Sam Willis tells the story of the English ruler who left the most indelible mark on the castle - the great Plantagenet king, Edward I, who turned it into an instrument of colonisation. Edward spent vast sums to subdue Wales with a ring of iron comprised of some of the most fearsome fortresses ever built. Castles like Caernarfon and Beaumaris were used to impose England's will on the Welsh. But when Edward turned his attention to Scotland, laying siege to castles with great catapults, things didn't go so well for him.

Sam Willis explores how, by the Wars of the Roses, castles were under attack from a new threat - the cannon - but survived into the Tudor era only to find their whole purpose challenged. What had once been strategic seats of power now had to keep up with the fickle fashions of the court and become palaces to impress monarchs such as Elizabeth I. Just as castles seemed to have lost their defensive function, the English Civil War erupted. The legacy of that tumultuous period resulted in castles no longer being associated with protection. Rather, their ruins took on a unique appeal, embodying a nostalgia for an age of chivalry that became a powerful part of the national psyche.