Peter I (, , ; 1068 - 1104) was King of Aragon and also Pamplona from 1094 until his death in 1104. Peter was the eldest son of Sancho Ramírez, from whom he inherited the crowns of Aragon and Pamplona, and Isabella of Urgell. He was named in honour of Saint Peter, because of his father's special devotion to the Holy See, to which he had made his kingdom a vassal. Peter continued his father's close alliance with the Church and pursued his military thrust south against bordering Al-Andalus taifas with great success, allying with Rodrigo Díaz de Vivar, known as El Cid, the ruler of Valencia, against the Almoravids. According to the medieval Annales Compostellani Peter was "expert in war and daring in initiative", and one modern historian has remarked that "his grasp of the possibilities inherent in the age seems to have been faultless."
Early life
The Crónica de San Juan de la Peña, a rather late source for Peter's reign, states that Peter was 35 years of age when he died, which places his birth in 1068 or 1069. As a child Peter was placed in the line of succession to the County of Urgell by the first testament of his uncle Ermengol IV, after Ermengol's own son and brothers. He was not destined to inherit it.
In 1085, two years after his father had conquered Graus (28 April 1083), Peter was entrusted with Sobrarbe and Ribagorza as a subkingdom with its capital at Graus, which he thenceforth ruled more or less independently with the title of king (Latin rex). On 28 October 1087 Peter joined his father in Pamplona in Navarre, where the two monarchs confirmed the rights of the bishops in the city. He pursued the Reconquista with vigour in the southeast of the realm. In 1087 he may have been present at the unsuccessful siege of Tudela. Later that year he conquered Estada, in 1088 Montearagón, and on 24 June 1089 Monzón. These conquests opened up the valley of the Cinca, which he proceeded to conquer as far as Almenar, taken in 1093.
Sole reign
Peter succeeded to the whole of his father's kingdom on the latter's death while besieging Huesca in 1094. Peter raised the siege, only to return to it within the year. After 1094 his objectives shifted westwards, towards the valley of the Gallega. In 1095 Peter renewed his father's oaths to Urban II, and Urban renewed his promise of protection, under which Sancho, his sons, and his kingdom had been placed in July 1089. On 16 March 1095 the pope even issued a bull, Cum universis sancte, granting the king and queen of Aragon immunity from excommunication without the permission of the pope. That same year, while he was besieging Huesca, Peter defeated the relief forces of the Taifa of Zaragoza at the Battle of Alcoraz. Peter later rewarded a certain Sancho Crispo for his contribution of three hundred knights and infantry at Alcoraz. He went on to take Huesca on 27 November of that same year.
Reconquista and war with the Almoravids
The next year (1096) Peter travelled south to inspect his fortress at Castellón, though the Historia Roderici claims that he came to help Rodrigo. He met Rodrigo in Valencia and with a large force already assembled they decided to reinforce the southern frontier fort of Benicadell, rebuilt by Rodrigo in 1091. As they were passing by Xàtiva they were met by an Almoravid force under the command of Mohammed, the nephew of Almoravid leader Yusuf ibn Tashfin, and the commander whom Rodrigo had defeated at the Battle of Cuarte in 1095. They decided to hastily restock Benicadell and retreat to Valencia via the coast, but were met at the Battle of Bairén by Muhammad's forces encamped on the high ground that reached almost to the sea. A small Almoravid fleet had been assembled from the southern ports, including Almería, and the Christians were trapped between arrow fire from the ships and the cavalry perched atop the hill. Rodrigo roused the troops with a speech and the next day at midday the Christians charged. The Battle of Xàtiva ended in a rout, with many Almoravids killed or forced into the river or the sea, where many drowned. Peter and Rodrigo returned to Valencia in triumph and thanking God for the victory, as the Historia records.
In 1099, in preparation for the fall of Barbastro, Peter sent Ponce, then Bishop of Roda, to Rome to ask Pope Urban II to transfer the see of Roda to Barbastro. The pope complied with Peter's request, and endowed the transferred diocese with all the re-conquered lands of the Diocese of Lleida. Peter's motive in this action was probably to curtail any expansion of the Diocese of Urgell in the direction of Lleida. In any case, Barbastro fell in 1100.