When his father Fulk died, Baldwin became king of Jerusalem. But at only 13 years of age Baldwin was too young to rule unaided. He was made co-ruler of the Crusader state along side his mother Melisende.

Baldwin III was old enough to rule Jerusalem unaided and demanded that the control he shared with his mother was ended. This split the Crusader state and led to civil war.

King Baldwin III laid siege to the port city of Ascalon. The city was surrounded and the only means of communications was by sea. Resupply was difficult by sea but the city had several wells to provide fresh water so the inhabitants were not easily pursuaded to surrender. The attackers built a tall tower near the walls so that they could fire over the defences into the streets. When the defenders set fire to the tower it collapsed taking part of the city walls with it allowing the Templars to enter the breach. But the knights were outnumbered and killed and the breach was repaired. The siege finally took its toll on the inhabitants and they agreed to surrender in return for safe passage.

Baldwin, the king of Jerusalem died. He was succeeded by his brother Amalric. ^[1]