Baldwin III., king of Jerusalem (1143-1162), was the eldest son of Fulk of Jerusalem by his wife Melisinda. He was born in 1130, and became king in 1143, under the regency of his mother, which lasted till 1152. He came to the throne at a time when the attacks of the Greeks in Cilicia, and of Zengi on Edessa, were fatally weakening the position of the Franks in northern Syria; and from the beginning of his reign the power of the Latin kingdom of Jerusalem may be said to be slowly declining, though as yet there is little outward trace of its decay to be seen. Edessa was lost, however, in the year after Baldwin's accession, and the conquest by Zengi of this farthest and most important outpost in northern Syria was already a serious blow to the kingdom. Upon it in 1147 there followed the second crusade; and in that crusade Baldwin III., now some eighteen years of age, played his part by the side of Conrad III. and Louis VII. He received them in Jerusalem in 1148; with them he planned the attack on Damascus and with them he signally failed in the attack. In 1149, after the failure of the crusade, Baldwin III. appeared in Antioch, where the fall of Raymund, the husband of the princess Constance, made his presence necessary.
He regulated affairs in Antioch, and tried to strengthen the north of Palestine generally against the arm of Zengi's successor, Nureddin, by renewing the old and politic alliance with Damascus interrupted since 1147, and by ceding Tellbashir, the one remnant of the county of Edessa, to Manuel of Constantinople. In 1152 came the inevitable struggle between the young king and his mother, who had ruled with wisdom and vigour during the regency and was unwilling to lay down the reins of power. Baldwin originally planned a solemn coronation, as the signal of his emancipation. Dissuaded from that course, he nevertheless wore his crown publicly in the church of the Sepulchre. A struggle followed: in the issue, Baldwin agreed to leave his mother in possession of Jerusalem and Nablus, while he retained Acre and Tyre for himself. But he repented of the bargain; and a new struggle began, in which Baldwin recovered, after some fighting, the possession of his capital. From these internal dissensions Baldwin was now summoned to the north, to regulate anew the affairs of Antioch and also those of Tripoli, where the death of Count Raymund had thrown on his shoulders the cares of a second regency.
On his return to Jerusalem he was successful in repelling an attack by an army of Turcomans; and his success encouraged him to attempt the siege of Ascalon in the spring of 1153. He was successful: the "bride of Syria," which had all but become the property of the crusaders in 1099, but had since defied the arms of the Franks for half a century, became part of the kingdom of Jerusalem. From 1156 to 1158 Baldwin was occupied in hostilities with Nureddin. In 1156 he had to submit to a treaty which cut short his territories; in the winter of 1157-1158 he besieged and captured Harim, in the territory once belonging to Antioch: in 1158 he defeated Nureddin himself. In the same year Baldwin married Theodora, a near relative of the East Roman emperor Manuel; while in 1159 he received a visit from Manuel himself at Antioch. The Latin king rode behind the Greek emperor, without any of the insignia of his dignity, at the entry into Antioch; but their relations were of the friendliest, and Manuel - as great a physician as he was a hunter - personally attended to Baldwin when the king was thrown from his horse in attempting to equal the emperor's feats of horsemanship.
In the same year Baldwin had to undertake the regency in Antioch once more, Raynald of Chatillon, the second husband of Constance, being captured in battle. Three years later he died (1162), without male issue, and was succeeded by his brother Amalric I.
Baldwin III. was the first of the kings of Jerusalem who was a native of the soil of Palestine. His three predecessors had all been emigrants from the West. His reign also marks a new departure from another point of view. His predecessors had been men of a type half military, half clerical - at once hard fighters and sound churchmen. Baldwin was a man of a subtler type - a man capable of dealing with the intrigues of a court and with problems of law, and, as such, suited for guiding the middle age of the kingdom, which the different qualities of his predecessors had been equally suited to found. Like his brother, Amalric I., he was a clerkly and studious king versed in law, and ready to discuss points of dogma. In an excellent sketch of Baldwin's character (xvi. cii.), William of Tyre tells us that he spent his spare time in reading and had a particular affection for history; that he was well skilled in the jus consuetudinarium of the kingdom (afterwards recorded by lawyers like John of Ibelin and Philip of Novara as "the assizes of Jerusalem"); and that he had the royal faculty for remembering faces, and could generally be trusted to address by name anybody whom he had once met, so that he was more popular with high and low than any of his predecessors.
He had, William also reports, a gift of impromptu eloquence, and a faculty both for saying witty things pleasantly at other people's expense and for listening placidly to witticisms directed against himself; while he was generous to excess without needing to make exactions in order to support his generosity, and always respected the Church. If in his youth he had been prone to gambling, and before his marriage with Theodora had been somewhat lax in his morals, when he became a man he put away childish things; his married life was a shining example to his people and he was abstemious both in food and drink, holding that "excess in either was an incentive to the worst of crimes." Even his enemy, Nureddin, said of him, when he died - "the Franks have lost such a prince that the world has not now his like."
William of Tyre is the great primary authority for his reign; Cinnamus and Ibn-al-athir (see Bibliography to the article Crusades) give the Byzantine and Mahommedan point of view. His reign is described by R. Röhricht, Geschichte des Königreichs Jerusalem (Innsbruck, 1898), C. xiii.-xvi.