The Roman baths and the first cathedral
Originally, under the current location of the cathedral, the Legio VII Gemina had built the baths, with a size larger than the current building.
Remains of the first cathedral were explored near the south facade in 1997.

During the Christian reconquest the ancient Roman baths were converted into a royal palace.
King Ordoño II, who had occupied the throne of Leon in 916, defeated the Arabs in the Battle of San Esteban de Gormaz in 917.
As a sign of gratitude to God for victory, he gave up his palace to build the first cathedral.
Under the episcopate of Fruminio II, the building was transformed into a sacred place.
The tomb of Ordoño II of Leon, who died in 924, is found in the cathedral.

The temple was guarded and governed by monks of the Order of St. Benedict, and it is likely that its structure was very similar to many others existing during the Leonese Mozarabic period.
Almanzor campaigned through these lands in the late 10th century, devastating the city and destroying the temples.
However, damage to the building of the cathedral appears to have been rapidly addressed, since in the year 999 King Alfonso V was crowned in the church.

After the political turmoil and Moorish raids that lasted till 1067 the state of the cathedral was in extreme poverty.
This would move to King Ferdinand I of León, who, after transferring the remains of San Isidoro to León, sought to restore the temple.
This king achieved success in the expansion of the kingdom.

The Romanesque cathedral
With the help of Princess Teresa Urraca of Navarre, sister of the king, the construction of a second cathedral, was started, and within its architecture.
It fell within the Pelayo II episcopal see.
Its style was essentially Romanesque, built in brick and masonry, with three naves finished in semicircular apses, the central one dedicated to Saint Mary, as in the previous church.
While the cathedral was built according to the international style, examination of what has survived of its original facade, its originally indigenous nature can be noted.
There is still the use of the horseshoe arch, at least decoratively.
The cathedral was consecrated on November 10, 1073 during the reign of Alfonso VI.
Presumably the same masons who were building the Basilica of San Isidoro of Leon worked on it.

This cathedral remained standing until the end of the next century.
When the last proprietary king of Leon, Alfonso IX, rose to the throne, the city and the kingdom witnessed major social, artistic, and cultural changes.
The Roman baths and the first cathedral
Originally, under the current location of the cathedral, the Legio VII Gemina had built the baths, with a size larger than the current building. Remains of the first cathedral were explored near the south facade in 1997.
During the Christian reconquest the ancient Roman baths were converted into a royal palace. King Ordoño II, who had occupied the throne of Leon in 916, defeated the Arabs in the Battle of San Esteban de Gormaz in 917. As a sign of gratitude to God for victory, he gave up his palace to build the first cathedral. Under the episcopate of Fruminio II, the building was transformed into a sacred place. The tomb of Ordoño II of Leon, who died in 924, is found in the cathedral.
The temple was guarded and governed by monks of the Order of St. Benedict, and it is likely that its structure was very similar to many others existing during the Leonese Mozarabic period. Almanzor campaigned through these lands in the late 10th century, devastating the city and destroying the temples. However, damage to the building of the cathedral appears to have been rapidly addressed, since in the year 999 King Alfonso V was crowned in the church.
After the political turmoil and Moorish raids that lasted till 1067 the state of the cathedral was in extreme poverty. This would move to King Ferdinand I of León, who, after transferring the remains of San Isidoro to León, sought to restore the temple. This king achieved success in the expansion of the kingdom. 
The Romanesque cathedral
With the help of Princess Teresa Urraca of Navarre, sister of the king, the construction of a second cathedral, was started, and within its architecture. It fell within the Pelayo II episcopal see. Its style was essentially Romanesque, built in brick and masonry, with three naves finished in semicircular apses, the central one dedicated to Saint Mary, as in the previous church. While the cathedral was built according to the international style, examination of what has survived of its original facade, its originally indigenous nature can be noted. There is still the use of the horseshoe arch, at least decoratively. The cathedral was consecrated on November 10, 1073 during the reign of Alfonso VI. Presumably the same masons who were building the Basilica of San Isidoro of Leon worked on it.
This cathedral remained standing until the end of the next century. When the last proprietary king of Leon, Alfonso IX, rose to the throne, the city and the kingdom witnessed major social, artistic, and cultural changes.
León Cathedral