The Royal Monastery of San Zoilo is the oldest Romanesque building in Carrión de los Condes. It was built over the remains of a Roman camp and the first evidence of its existence dates back to the year 948. The abbey has kept the relics of saint Zoilo since 1047. In the Middle Ages it was one of the most important abbeys; it was the seat of the court of the kings of Castile and León and served as a meeting place for several councils.
Likewise, the monastery housed many tombs of noblemen. When the Cluniac Order took possession of it in 1076, the abbey became a focal point of the Cluniac reform. The expropiation of 1835 caused the dissolution of the Benedictine community that governed the temple at that time. Since then, the construction has served as a seminary and an educational centre. Today it houses a hotel. The abbey was declared an Artistic and Historic National Monument on 3rd June, 1931.
It was during the restoration the temple underwent in the 16C that the present Gothic-Renaissance cloister was built. Nevertheless, the original buildings of the abbey can still be seen.
The main front, with a basket-handle arch and archivolts, was created in the late Gothic style. It is ornamented with Franciscan cords. The interior is covered with a wood frame; and the high altar with a Gothic groin vault. In the 17 C both structures were covered with plaster in the manneristic style. The present temple is Baroque, and it contains the sepulchres of the infamous Infants of Carrión, protagonists of the black legend in the Cantar de Mío Cid.
In 1993 took place the discovery of a Romanesque portal on the west wall of the original church. It was in an excellent state of preservation. It consists of two superimposed semicircular archs, flanked by 2 C Roman marble columns. Its four capitals are decorated with religious scenes and inscriptions, carved on three sides over plain or fluted muticoloured Italian shafts and Romanesque bases. On the door can be read the consecration inscription of the temple.