Sir John Fastolf was real, and so was the man Shakespeare turned him into. Fastolf served in France through some of the bitterest fighting of the Hundred Years War, accumulated wealth from ransoms and royal favour, and came home to spend it on Caister. His name and reputation - along with that of Sir John Oldcastle, a Lollard knight executed in 1417 - became the raw material for Shakespeare's Falstaff. The play turned a competent if controversial soldier into English literature's most beloved coward and drunk. Fastolf himself would probably have been irritated; the castle he built was meant to be a monument to military success, not a punchline. He intended after his death in 1459 that it become an enormous chantry, where priests would pray for his soul forever.

Fastolf died childless and intestate. The legal mess that followed produced one of the most extraordinary documents in English history. John Paston, Fastolf's confidant and advisor, claimed the castle as his inheritance. So did the Duke of Norfolk. So did Sir William Yelverton. While they fought it out, the Paston family wrote letters - to each other, to their lawyers, to allies and enemies - documenting their struggles in plain English over two generations. The Paston Letters survived. They give modern historians a uniquely intimate view of late medieval England, of a family clawing its way up the social ladder during the Wars of the Roses. The bulk of Fastolf's money went to endow Magdalen College, Oxford. The castle went to the Pastons, eventually, after they had fought for it.

In August 1469, the Duke of Norfolk decided to take the castle by force. John Paston junior held it with about thirty men. The siege lasted two months. The Pastons ran out of food and ammunition. One of the family's longest-serving servants died from a crossbow bolt. When the castle fell, the Pastons lost everything they had been fighting to keep. The letters from those weeks survive: appeals for help, accusations of betrayal, requests for gunpowder that arrived too late or not at all. Years later the family recovered the castle. But the siege of 1469 - thirty men against a duke's army, two months of brick walls and dwindling supplies - remains one of the few medieval English sieges where we can read the besieged's own letters.

Most of the castle fell into ruin after 1600 when a new house was built nearby. The tower did not. It stands today essentially intact, climbable by visitors, offering views over the flat fields where Fastolf's masons once worked. The inner moat was filled in between 1842 and 1893. In 1776, a Reverend David Collyer removed a 122-step newel staircase from the tower and reinstalled it in his house at Wroxham - a private theft of medieval architecture nobody seems to have stopped. In the 1960s the castle's owners opened a Motor Museum in the southwest grounds: veteran, vintage, classic and sports cars, horse-drawn vehicles, bicycles, pedal cars and agricultural equipment, all displayed in a purpose-built building. Visit Caister Castle today and a single admission ticket gets you the brick tower Sir John Fastolf built and a hangar full of automobiles. Six centuries collapse into a single afternoon.