THE REFORM OF THE DIVINE OFFICE IN THE MONASTERY OF SAN ISIDORO DE LEON THROUGH THE BREVIARY OF 1475

The canonical community established in the monastery of Saint Isidor of Leon from the middle of the 12th century effectuated a singular reform of the Divine Office in the latter part of the 15th century, almost unknown to researchers. This article, on the one hand, will attempt to present the criteria adopted in the reform using the ms. 36 from the Archivo de la Real Colegiata. This breviary, copied in 1475 commissioned by Abbot Juan Alvarez de Valdesalce (1458-1482), constitutes an exceptional testimony that permits the deciphering of the modus operandi of the Isidorian canons in the renovation of the two principal liturgical sections: Proper of the Time and Proper of Saints. On the other hand, the author will examine the historical documentation in order to identify the motives that pursuaded the Leonese canons to embrace the liturgical tradition of the congregation of Saint Rufus of Avignon.