In the epic 2005 Hollywood film. Kingdom of Heaven, the noble leper king dies peacefully in his Jerusalem palace, remembering how – aged only 16 – he had defeated Saladin. The scene’s fin de siècle feel is spot on. Baldwin’s death heralded the end of an era. Within a decade, Saladin would rout the squabbling Crusaders at Hattin, and march virtually unopposed to take Jerusalem as his prize.

But just over seven years earlier, it had all been so different. The victory King Baldwin IV was recalling was the epic Battle of Montgisard, which took place on 25 November 1177.

Saladin was the first existential threat the Crusader Kingdom had faced since its foundation in 1099. Born in Tikrit (home of Saddam Hussein), he had seized power in Egypt, imposed Sunni Islam on the Shia population, and slowly built an empire. When the powerful Nur ad-Din of Aleppo died in 1174, Saladin consolidated his power from Cairo and Yemen in the south up to the Turkish border. The only thorn in his side was the narrow strip of land controlled by the Crusaders.

In 1177 he moved out of Egypt to march on Jerusalem. Believing the Crusaders were unable to field an army to oppose him, his discipline was slack, and he let his troops spread out and forage. It was a fatal mistake.

King Baldwin IV mustered his troops at Ascalon (just north of today’s Gaza Strip). Alongside him was Raynald of Châtillon, a.k.a. the Elephant of Christ. Balian of Ibelin was there, too, although – unlike in the film – he was not a doe-eyed blacksmith from France, but a lifelong member of the Crusader warrior-aristocracy on both his father’s and mother’s sides. Among the several hundred others that rode in the royal host, Brother Odo of St Amand, Grand Master of the Knights Templar, led a division of 84 battle-hardened Templars from Gaza. The Bishop of Bethlehem carried the True Cross.

Baldwin’s army broke out of Ascalon and marched to cut Saladin off from reaching Jerusalem. When the enemy came in sight, Baldwin dropped to his knees before the True Cross and prayed.

It is not possible to know the exact numbers that faced each other. The chronicler William of Tyre says Baldwin had 375 knights plus the Templars against Saladin’s 26,000 knights. These estimates are certainly wrong, but the picture of dramatic numerical imbalance is clear.

The armies closed at Montgisard, near Ramla. Saladin was taken totally by surprise. His baggage train was floundering in a bog, and his forces were still scattered. The 16-year-old king fought in the thick of the press, his hands and arms swathed in bandages. Chroniclers say that St George fought alongside him.

The result was decisive. Saladin’s forces were decimated in the heaviest defeat of his career. Overconfidence had undone him, leaving his prestige heavily damaged. Only a small fraction of his invasion army survived to accompany him on the long trek back across the Sinai to Cairo.

In the end, the Muslims’ vast resources of wealth and manpower were far greater than the Crusaders’, and the final result of the civilisational clash was never in question. But it would take Saladin another 10 years to expel the Crusaders from Jerusalem, and others would spend another hundred years pushing the Crusaders out of the Near East completely. For the time being, the unlikeliest of teenage rulers had saved the kingdom.