On the 8th of February, 1250, a battle took place twenty leagues from Damietta, at Mansourah (the city of victory), on the right bank of the Nile.

The king's brother, Robert, Count of Artois, marched with the vanguard, and obtained an early success; but William de Sonnac, grand master of the Templars, and William Longsword, Earl of Salisbury, leader of the English crusaders but lately arrived at Damietta, insisted upon his waiting for the king before pushing the victory to the uttermost.

Robert taxed them, ironically, with caution.
"Count Robert," said William Longsword, "we shall be presently where thou'lt not dare to come nigh the tail of my horse." There came a message from the king ordering his brother to wait for him; but Robert made no account of it." I have already put the Saracens to flight," said he, "and I will wait for none to complete their defeat; "and he rushed forward into Mansourah.

All those who had dissuaded him followed after; they found the Mussulmans numerous and perfectly rallied; in a few moments the Count of Artois fell, pierced with wounds, and more than three hundred knights of his train, the same number of English, together with their leader, William Longsword, and two hundred and eighty Templars, paid with their lives for the senseless ardor of the French prince.
The king hurried up in all haste to the aid of his brother; but he had scarcely arrived, and as yet knew nothing of his brother's fate, when he himself engaged so impetuously in the battle that he was on the point of being taken prisoner by six Saracens who had already seized the reins of his horse.

He was defending himself vigorously with his sword, when several of his knights came up with him, and set him free.