On so-called "Black Monday" in 1360, a hail storm kills an estimated 1,000 English soldiers in Chartres, France. The storm and the devastation it caused also played a part in the Hundred Years' War between England and France.
The Hundred Years' War began in 1337; by 1359, King Edward III of England was actively attempting to conquer France. In October, he took a massive force across the English Channel to Calais. The French refused to engage in direct fights and stayed behind protective walls throughout the winter, while Edward pillaged the countryside.
In April 1360, Edward's forces burned the Paris suburbs and began to move toward Chartres. While they were camped outside the town, a sudden storm materialized. Lightning struck, killing several people, and hailstones began pelting the soldiers, scattering the horses. One described it as "a foul day, full of myst and hayle, so that men dyed on horseback [sic]." Two of the English leaders were killed and panic set in among the troops, who had no shelter from the storm.
The heavy losses suffered by the English were seen by many as a sign from God. King Edward was convinced to negotiate peace with the French. On May 8, 1360, the Treaty of Bretigny was signed, marking the end of the first phase of the Hundred Years' War. Edward agreed to renounce all claims to the throne of France, though he was given control of land in the north of the country. Fighting resumed nine years later, when the king of France declared war, claiming Edward had not honored the treaty. The last phase of the Hundred Years' War did not end until 1453.
The largest hailstone recorded in modern times was found in Aurora, Nebraska. It was seven inches in diameter, about the size of a soccer ball. Hail typically falls at about 100 miles per hour.