The siege of Kenilworth began on June 25, 1266. Kenilworth had been a royal castle, fortified by King John, the father of King Henry III. Once his father died and Henry himself ascended the throne, he gave it as a gift to Simon de Montfort, his brother-in-law, potentially in an attempt to insure his loyalty. That decision came back to haunt him as the castle was one of the strongest fortifications in England, and included a lake or ‘mere’.
After Simon’s defeat and subsequent death at Evesham, the last holdouts in the war retreated to Kenilworth, and when Henry attempted to negotiate with the defenders, they sent back his messenger without his hand.
By the time the royal forces assembled at Kenilworth Castle, the garrison – who probably numbered about 1,200, including wives, children and servants – had built up stocks of enough food to hold out for months. They also had siege engines, which, according to a contemporary chronicler, were ‘hitherto unheard of among us and unseen’. The king, for his part, had also amassed a huge arsenal of weaponry – including 2,000 wooden ‘hurdles’, which were screens to protect the royal soldiers from missiles, 60,000 crossbow bolts and nine siege engines. Some of the stone balls thrown by the siege engines at Kenilworth weighed up to 140 kilos and were found by archaeologists in the 1960s.
Starting that day in June, the king began bombarding the castle with what has been described as a continuous stream of missiles. Their efforts were thwarted, however, by the superior range of the weaponry inside. One chronicler described the stone projectiles from the two sides ‘clashing in the air’. As a result, the king had to send to London for larger siege engines, one of which, a siege tower large enough to contain 200 crossbowmen, was rendered useless by a well-aimed missile.
The water defenses also foiled the attempts on the part of the royal forces to undermine the castle walls. Thus, the king hauled barges overland from Chester in hopes of assaulting the castle from the mere. These attempts were also thwarted by the defenders.
Knowing his authority was daily being undermined, and desperate to restore his prestige, he called a parliament near the castle in October. This resulted in the peace terms known as the Dictum of Kenilworth, issued on 31 October, returning forfeited lands to the rebels provided they paid heavy fines. Even with this agreement, the garrison fought on another six weeks.
In the end, with Henry ordering further forces to prepare to storm the castle, the defenders were suffering too much from disease and starvation. Thus on the 13 of December 1266, the remnants of the garrison submitted to the terms they had been offered in October. Henry even allowed them to leave with their arms, horses and harness. Only two days’ supply of food remained in the castle.
At 172 days, thus ended the longest siege in English medieval history.
The victory shortlived for Henry. Though Kenilworth Castle was restored to him, his opponents quickly started up trouble elsewhere, in large part because of the vindictiveness of the royalists once they were released. It took another year to fully end the civil war.
The siege was also ruinously expensive, leaving Henry so short of money that he had to pawn the jewels from the shrine of King Edward the Confessor in Westminster Abbey.
Perhaps the siege’s greatest impact was on Prince Edward, who succeeded his father in 1272 as King Edward I. At Kenilworth Castle he had seen the full array of the latest weaponry pitted against a formidable modern fortress, in a type of warfare refined by crusaders in the Middle East and France. This direct experience of how castles worked informed his thinking in time for the crusades he embarked on in 1270 and his great castle-building (and besieging) campaigns from 1277 onwards in Wales and Scotland.