Don, king of Portugal, succeeded his brother Don Sancho II. in the year 1248. In the course of a war with the Moors, which he engaged in at the beginning of his reign, he considerably extended the Portuguese dominions. He took possession of the city of Fara, the capital of the Moorish kingdom, in the province of Algarve. Loula, another Moorish town, which was carried by storm, also fell into his hands. His power was thus extended abroad by the success of his arms, and the administration of his affairs at home became prosperous and popular by his wisdom and prudence. But the tranquillity and prosperity of the kingdom was somewhat disturbed by an interdict which it was put under by Pope Alexander IV. whose displeasure he had incurred by marrying Donna Beatrix, the natural daughter of Don Alonso the Wise, king of Castile, while his first wife was living. In 1262, when his first queen died, the interdict was removed by Pope Urban, a dispensation was granted, and the children of Donna Beatrix were legitimated. Hitherto frequent disputes had occurred between the kings of Portugal and Castile relating to the boundaries of the two kingdoms. To terminate all differences on this subject, and to prevent them in future, commissioners were appointed to define and settle the limits of their respective dominions; and these were agreed to and acknowledged by a solemn deed.

Encouraged by the prosperity of his kingdom, and by the success which had attended his enterprises, Alphonsa made an attempt to extend the influence of the crown, by obliging the clergy to contribute to the welfare of the state. But this measure, as might have been expected, was not quietly submitted to. It occasioned the revival of old disputes, the pope interfered, and in 1268 the kingdom was again laid under an interdict. He succeeded, by the wisdom of his negociations, in obtaining from Castile an exemption of all claims upon the crown of Portugal, and in procuring an acknowledgement that its monarchs were entirely relieved from the performance of every kind of homage. He died in the year 1279, in the 69th year of his age, and in the 31st of his reign. Before his death, he was reconciled to the pope and clergy, having made a full and ample submission. This prince was tall in stature, of a prepossessing aspect, and of engaging manners. Alike removed from a disposition to extravagant expense or sordid avarice, in times of peace and prosperity he could indulge in magnificence; but when his affairs required it, he failed not to regulate them by frugality and economy. To the poor he was a sincere friend. In a time of scarcity he pawned his crown to provide them with bread. His steady and vigorous administration secured to him the respect of the nobles and the obedience of the clergy. (Mod. Univ. Hist.)