Sahagún's San Benito Imperial Monastery. From Tierra de Campos to Liébana and Segovia, it was a major mediaeval monastery. When Cluny control came to the Iberian Peninsula, it was a major Benedictine monastery reform centre. The monastery declined in the 15th century after San Benito de Valladolid was founded and reformed. The monastery was burned down multiple times during revolts and disentailment in the 19th century due to the town of Sahagún's power struggle over the people.

Spain submitted a "Inventario Retrospectivo - Elementos Asociados" to UNESCO in 2015 to support the extension of the Way of St. James to "Caminos de Santiago de Compostela: Camino francés y Caminos del Norte de España." The convent of San Benito was included as number 1428.

Alfonso III the Great bought a church on the spot where the martyr saints Facundo and Primitivo were venerated to give it to Abbot Alonso, who was fleeing Cordoba's Christian persecution. In 904, Alfonso III gave Abbot Alonso Calzada, the earliest written record of the monastery.

Alfonso VI chose this monastery to take the habit and practise before becoming king, which was the abbey's golden age. His marriage to Constance of Burgundy, who was French and interested in implementing Roman liturgy, brought Cluny monks to the abbey. Alfonso VI named the Frenchman Don Bernardo of Aquitaine as abbot in 1080, and in 1085 he awarded Sahagún the famous charters, which helped the town expand under the abbey's control. The abbot's power became so much that the king gave up control over the monastery's Holy See-dependent region.