A frontier county on the Douro and Minho, governing the region around Porto and Guimarães where Portuguese identity first formed; held from the mid-9th century as a vassal fief of the kingdoms of Asturias, Galicia and León, then re-granted in 1096 by Alfonso VI of León to his son-in-law Henry of Burgundy after an earlier rebellion had lapsed the title.
Henry's son Afonso Henriques proclaimed himself King of Portugal after the Battle of São Mamede (1128) and the Battle of Ourique (1139); León recognized the new kingdom's independence by the Treaty of Zamora in 1143.
Standard English-language survey covering the county's formation under Asturias/León/Galicia overlordship and Henry of Burgundy's 1096 re-establishment through to independence.