During his episcopal tenure he oversaw the most productive scriptorium in Spain, which produced the vast Corpus Pelagianum,[1] to which Pelagius contributed his own Chronicon regum Legionensium ("chronicle of the Kings of León").
His work as a historian is generally reliable, but for the forged, interpolated, and otherwise skilfully altered documents that emanated from his office he has been called el Fabulador ("the Fabulist")[2] and the "prince of falsifiers".
The Liber testamentorum includes a genealogy that suggests that Pelagius may have been related to the western Asturian families that founded the monasteries of Coria and Lapedo.
[8] At the same time (1104), Pelagius engaged in lawsuits with the count Fernando Díaz, the countess Enderquina Muñoz, and the abbot of Corias to maintain his rights of seignory within Asturias.
[9] He was also involved in jurisdictional battles with the neighbouring sees of Burgos (over Asturias de Santillana) and Lugo, and between 1109 and 1113 had to fight off the metropolitan claims of the Archdiocese of Braga as well.
She in turn made grants to Oviedo on three separate occasions, in 1112, 1118, and 1120 and Pelagius was the dominant Asturian at court, confirming fifteen royal charters during her reign.
[12] In 1130 Pelagius was deposed by a synod held under Cardinal Humbert at Carrión, along with Diego and Munio, bishops of León and Salamanca, and the abbot of Samos, because they had opposed the marriage of Alfonso VII and Berenguela of Barcelona (1127) on grounds of consanguinity.
[13] During the last decades of the eleventh century and the first of the twelfth, Santiago de Compostela became one of the leading centres of pilgrimage among the Catholic faithful, aided by the efforts of its archbishop, Diego Gelmírez.
The rivalry between Pelagius and Diego can be seen in the former's attempt to establish Oviedo as a comparable destination for pilgrims, by expanding the cult of the relics of the Cathedral of San Salvador, most importantly the alleged Sudarium of Christ.
[18] Pelagius' original Chronicon[19] was composed as a continuation of a series of chronicles which he gathered together and had copied into the Liber chronicorum, the principal part of the Corpus Pelagianum.
Pelagius' original chronicle, that known as Chronicon regum Legionensium, was completed sometime after 1121, since it refers to the marriage of Alfonso VI's daughter Sancha to Rodrigo González, who is given the title Count.
[23] Pelagius' Chronicon is mostly interested in ecclesiastical history, especially that of his province, and its description of royal activity is barren, rarely amounting to more than a list of successes, such as cities conquered.
Pelagius also had all judicial documents relating to the diocese collected and copied into a massive cartulary called the Liber testamentorum or Libro (gótico) de los testamentos, compiled around 1120, possibly at the monastery of Santos Facundo y Primitivo in Sahagún.
[26] Though it contains falsified, forged, and interpolated documents designed to buttress the claims of Oviedo, otherwise it remains an important compilation for historical research.