Baldwin III (1143–1163) wrested sole rule from his mother Melisende, took Ascalon in 1153 — the kingdom's last great conquest — and bound Jerusalem to Byzantium by his Komnenian marriage.
Baldwin III was crowned at thirteen jointly with his formidable mother Melisende, and the kingdom nearly came to civil war when the grown king demanded reality to match the title: in 1152 he took Jerusalem from her partisans within a fortnight, then — the measure of them both — restored her to honour and counsel.
His reign carried the Second Crusade's wreckage (he was in the council that chose the disastrous Damascus attack of 1148), answered it with the five-month siege that finally took Ascalon (1153), and met Nur ad-Din's unification of Muslim Syria with the only counterweight available: the Byzantine marriage — Theodora Komnene, and with her the emperor Manuel's protection.
Born in 1130 to Fulk of Anjou and Melisende, Baldwin was the first king of Jerusalem born in the kingdom itself. His father's death in a hunting accident in 1143 made him king at thirteen under his mother's co-rule — an arrangement his grandfather Baldwin II had constitutionally designed, and which Melisende had every intention of making permanent.
His military schooling was immediate: Edessa fell to Zengi the next year, triggering the Second Crusade, and the teenage king campaigned in its humiliations — including the four-day fiasco before Damascus in 1148 that he had helped counsel.
William of Tyre, who knew the court and wrote the reign, drew Baldwin at full length and with love: tall, well-made, laughing easily, the best-lettered of Jerusalem's kings, a listening ruler who kept even his enemies' respect and — pointedly, in Outremer — kept his hands off other men's wives and the church's treasury. The vices conceded are gambling in his youth and a tongue too quick for dignity.
The crisis of 1152 shows the steel under the charm: refused real power at twenty-two, he demanded partition, took the north, then swept his mother's half in two weeks of actual siege warfare — Nablus, Jerusalem, the Tower of David — without an execution, a blinding, or a lasting breach; Melisende emerged dowager-counsellor rather than prisoner. Even his death played to character witnesses: the emirs, William says, held their raids while the kingdom carried its king to the Sepulchre.
Ascalon was the strategic prize of a decade: the last Fatimid port on the Palestinian coast, the standing threat to the kingdom's southern roads. Baldwin closed it inside the new castles — Ibelin, Blanchegarde, Gaza given to the Templars — and in January 1153 sat down before it with the whole kingdom, patriarch and True Cross included. The five-month siege survived the Templars' catastrophic private assault through the August breach; the city fell on 22 August, and the county of Jaffa-Ascalon went to his brother Amalric.
Against Nur ad-Din — master of Aleppo and, from 1154, of Damascus, the first union of Muslim Syria in crusader memory — Baldwin's answer was Constantinople: the marriage to Manuel I's niece Theodora in 1158 (she was thirteen, the treasury got 100,000 hyperpyra), the joint Antioch settlement of 1159 that put the emperor in ceremonial lordship over the principality, and the unbuilt but real deterrent of Byzantine power that held the north together for a generation.
Baldwin sickened through 1162 and died at Beirut on 10 February 1163, thirty-three and childless; the lozenges prescribed by his Syrian doctor fed the usual poison rumour, which William of Tyre reports and doubts. The funeral cortège to Jerusalem drew, the chronicler insists, Muslim mourners down from the hills, and Nur ad-Din declined to profit: the Franks, he reportedly said, had lost such a prince as the world no longer had.
The succession went, after baronial argument, to Amalric — on condition he shed his wife Agnes de Courtenay, whose children were nonetheless kept legitimate: a lawyer's compromise whose consequences (Baldwin IV, Sibylla, and through Sibylla, Guy of Lusignan and Hattin) would unmake the kingdom within a quarter-century. Baldwin III's own balance — Ascalon taken, Byzantium bound, the barons managed, the mother honoured — marked the kingdom's high water; the tide behind it was already Nur ad-Din's.