|The Wash, with Norfolk on right and Lincolnshire on left|
It was a confrontation with French forces that would lead not only to his death, but to perhaps his greatest embarrassment as a king: the loss of the Crown Jewels—not through actions of the enemy, but through lack of caution or proper planing ahead. Some of the Barons, once again fighting with John, invited Prince Louis of France to lead them: he had a slim claim to the throne because of his marriage to a granddaughter of Henry II (John's father). Louis landed with his army at Kent and proceeded to take over parts of the southeast.
There was fighting all over. John ended a siege on Windsor Castle and moved toward London to clear out the rebels, then north to end a siege at Lincoln, then to Bishop's Lynn* in Norfolk (see the graphic above). While there, he contracted dysentery; this was in late September. As if that weren't enough, King Alexander II of Scotland (1198-1249) took advantage of the turmoil in England to head south, conquering as he came and intending to swear loyalty to Prince Louis in exchange for holding England.
John, still very ill, headed west from Norfolk with his troops, but sent his baggage train across the lowlands of The Wash, the square-shaped estuary marked in yellow in the above graphic. While traversing the causeway and ford during low tide, the slow-moving wagons got caught in the sand, and were overtaken by the cold North Sea waters. The Crown Jewels, and who knows how many other goods and men, were lost in The Wash on 12 October 1216. A week later, John lost his life. He was succeeded by his son, King Henry III, who reigned 56 years until 1272.
*Now renamed "King's Lynn" thanks to Henry VIII.