Afonso I of Portugal in the context of Theresa of Portugal, Countess of Flanders

Portuguese participation in the Reconquista occurred from when the County of Portugal was founded in 868 and continued for 381 years until the last cities still in Muslim control in the Algarve were captured in 1249. Portugal was created during this prolonged process and largely owes its geographic form to it.

The Portuguese Reconquista involved the participation of north European crusaders passing through Portuguese coasts en route to the Holy Land, such as Englishmen, French, Flemings, Normans and Germans, most notably at the conquest of Lisbon in 1147, but also in 1142, 1154, 1189, 1191 and 1217. Many settled in Portugal at the invitation of king Afonso I or his son and successor Sancho I.

Manifestis Probatum (Latin for 'Manifestly proven') is a papal bull and the founding document of Portugal. On 23 May 1179 Pope Alexander III promulgated the bull. The bull officially recognized the independence of Portugal from Leon by confirming the Kingdom of Portugal to the now-recognized king Afonso Henriques and his successors. The bull is, therefore, the single most important written document from Portugal's independence process.

The Papacy did not recognize the legitimacy of Afonso's adoption of the royal title in 1139, and continued to regard him as a vassal of the kingdom of León. On December 13, 1143, Afonso wrote Pope Innocent II the letter Claves Regni (Latin for 'Keys of the Kingdom'), declaring his decision to enfeoff Portugal to the Holy See and asking for protection against any interference in Portugal's territory. On May 1, 1144, Pope Lucius II replied by letter Devotionen Tuam (Latin for 'Your Devotion') and stated that he recognized Afonso's devotion, but still referred to Portugal as a land instead of a kingdom, and to Afonso as duke instead of a king.

The Iberian Crusades were papally promoted wars, part of the Reconquista, fought against the Muslim states of the Iberian Peninsula within the wider Crusading movement from 1095 to 1492. The Muslim conquest of the peninsula was completed in the early 8th century, when the Christian Visigothic Kingdom fell, yet the small realm of Asturias endured in the north-west. From the 9th century, its southward expansion against al-Andalus (Muslim Spain) was portrayed in local chronicles as a divinely sanctioned war of recovery. This expansion, along with Frankish advance, gave rise to new Christian realms—Navarre, León, Aragon, Castile, Portugal, and Barcelona—in the north. After al-Andalus split into taifas (small states) in 1031, the Christian realms exploited Muslim disunity to further expansion. From the 1060s, the papacy occasionally supported campaigns against al-Andalus by granting spiritual rewards to participants.

As the Reconquista advanced, the taifa rulers sought aid from the fundamentalist Almoravids of North Africa, who halted the Christian expansion. Soon after proclaiming the First Crusade for the liberation of the Holy Land at the Council of Clermont in 1095, Pope Urban II extended the same spiritual privilege—remission of sins—to Iberian lords who took up arms against the Moors (Iberian Muslims). Peter I of Aragon was the first ruler, in 1100, to fulfil his crusading vow within the peninsula, and his example was soon followed by others. Leading crusading armies, Alfonso I of Aragon captured Zaragoza (1118), Afonso I of Portugal seized Lisbon (1147), and Ramon Berenguer IV of Barcelona took Tortosa (1148). The renewed Christian advance provoked another North African intervention, this time by the Almohads, who could only temporarily halt the Christian expansion. Occasionally, the Moors' Christian allies, such as Alfonso IX of León were also targeted by crusading campaigns. After crusader forces inflicted a decisive defeat on the Almohads at the Battle of Las Navas de Tolosa in 1212, the Reconquista gained new momentum. Papal grants of crusade indulgence then supported James I of Aragon in the conquest of Mallorca (1231) and Valencia (1238), and Ferdinand III of Castile in the capture of Córdoba (1236) and Seville (1248), reducing al-Andalus to the Emirate of Granada by 1262.

The Battle of São Mamede (Portuguese: Batalha de São Mamede, pronounced [ˈsɐ̃w mɐˈmɛðɨ]) took place on 24 June 1128 near Guimarães and is considered the seminal event for the foundation of the Kingdom of Portugal and the battle that ensured Portugal's independence. Portuguese forces led by Afonso Henriques defeated forces led by his mother Teresa of Portugal and her lover Fernão Peres de Trava. Following São Mamede, the future king styled himself "Prince of Portugal". He would be called "King of Portugal" starting in 1139 and was recognised as such by neighbouring kingdoms in 1143.

The Portuguese House of Burgundy (Portuguese: Casa de Borgonha) was a Portuguese noble house that ruled the County and later Kingdom of Portugal from its founding until the 1383–85 Portuguese Interregnum.

The house was founded by Henry of Burgundy, who became Count of Portugal in 1096. His son, Afonso Henriques, was proclaimed King of Portugal following his victory at the Battle of Ourique in 1139, establishing the Afonsine dynasty (Dinastia Afonsina). Burgundian monarchs would rule Portugal through much of its early formation, including the formalization of the Portuguese language under King Dinis I, the first Portuguese parliament, under King Afonso II, and the conquest of the Kingdom of the Algarve, under King Afonso III. Numerous princes of the house took up thrones across Europe, such as Ferdinand I, Count of Flanders and Peter I, Count of Urgell. Similarly, many princesses became royal consorts, including Berengaria, Queen of Denmark, Leonor, Queen of Aragon, and Teresa, Duchess of Burgundy, among others.

Sancho I (born Martinho; Coimbra, 11 November 1154 – 26 March 1211) also referred to as Sancho the Populator ("Sancho o Povoador"), was King of Portugal from 1185 until his death in 1211. He was the second king of Portugal.

Sancho was the second but only surviving legitimate son and fifth child of Afonso I of Portugal by his wife, Matilda of Savoy. Sancho succeeded his father and was crowned in Coimbra when he was 31 years old on 9 December 1185. He used the title King of Silves from 1189 until he lost the territory to Almohad control in 1191.

The Treaty of Zamora was a diplomatic meeting held on 4–5 October 1143 between Afonso Henriques, then styled Infante of Portugal, and his cousin Alfonso VII of León, King of León and Castile. It took place at the Cathedral of Zamora in the presence of the papal legate, Cardinal Guido de Vico.