Alfonso I (ca. 1109-1185) was the first king of Portugal. An accomplished warrior, he won independence from Castile and enlarged his realm at the expense of the Moslems.

Alfonso Henriques was born at Guimarães in the castle of his father, Henry of Burgundy, Count of Portugal. His ambitious mother, Teresa, daughter of Alfonso VI of León and Castile, ruled the county as regent after Henry died in 1112. When Alfonso rebelled against his mother in 1127 and took control of the county, he immediately faced an invasion by his cousin, the new king of León, Alfonso VII. The Leónese king refused to recognize the independence of Portugal until 1143, when Alfonso Henriques became a vassal of the pope; the two cousins then signed a treaty in Zamora under the auspices of the Church.

Alfonso was now free to enlarge his domain by conquering...