The Cathedral of Santa María de Regla de León is a temple of Catholic worship, the episcopal seat of the diocese of León, Spain, consecrated under the invocation of the Virgin Mary. It was the first monument declared in Spain by Royal Order of August 28, 1844 (confirmed by Royal Order on September 24, 1845).
Begun in the 13th century, it is one of the great works of the Gothic style, with French influence. Known by the nickname of Pulchra leonina, which means 'Bella Leonesa', it is located on the Camino de Santiago. 
The cathedral of León is known above all for taking to the extreme the "dematerialization" of Gothic art, that is, the reduction of the walls to their minimum expression to be replaced by colored stained glass, constituting one of the largest collections of medieval stained glass in the world. .
The Roman Baths
Originally, in the current location of the cathedral, the Legio VII Gemina had built some baths, with a size greater than the current building. During the major restoration of the building that took place in the 19th century, its remains were discovered under the cathedral, and in 1996 others were explored along the south façade. Little remains of these primitive buildings, just a few vestiges of mosaics, tegulas and ceramics, today exhibited in the cathedral museum. Others, like the hypocaust, still remain under the cathedral site.
The primitive cathedral
During the Christian reconquest, the old Roman baths were converted into a royal palace. In the year 916 King Ordoño II, who a few months ago had occupied the throne of León, defeated the Arabs in the battle of San Esteban de Gormaz. As a sign of gratitude to God for the victory, he gave the palace to him to build the first cathedral. Under the episcopate of Fruminio II, the building was transformed into a sacred place. The temple was guarded and governed by monks of the order of San Benito, and it is very likely that its structure was very similar to that of so many others that existed during the Leon mozarabic period. Following the Christian tradition of burying inside the temples those who embodied the "coming of God" authority, that simple cathedral was soon enriched with the remains of King Ordoño II, who died in Zamora in 924.
The chronicles of the passage of Almanzor through these lands at the end of the 10th century speak, devastating the city and destroying its temples. However, it seems that the damage caused to the cathedral's factory should have been immediately repaired, since in 999 King Alfonso V. was crowned there. After a succession of political revolts and harsh warfare, around 1067 the state of the cathedral was extremely poor. This would move King Ferdinand I of León, who, after transferring the remains of Saint Isidore from Seville to León, "turned to favors to it." With this king a peaceful time began, reaping great triumphs in the expansion of the Christian kingdom. It was the moment of the flowering of Romanesque art.
The Romanesque Cathedral
With the help of the Infanta Urraca de Zamora, the king's eldest daughter, the construction of a second cathedral began, in accordance with the aspirations of the city, and in the Romanesque style. Pelayo II occupied the episcopal see. When the architect Demetrio de los Ríos, between 1884 and 1888, excavated the basement of the cathedral to replace the pavement and cement the pillars, he found part of the walls and factory of that second cathedral. Through the plan that he himself drew, we can appreciate how everything was configured within the Gothic: it was made of brick and masonry, with three naves finished in semicircular apses, the central one dedicated to Santa María, as in the previous church. A cloister was also built on the north side. This new