The Real Colegiata Basilica de San Isidoro or, simply, San Isidoro de León, is a Christian temple located in the city of León.

It is one of the most outstanding Romanesque-style architectural ensembles in Spain, for its history, architecture, sculpture, and for the Romanesque luxury objects that have been preserved.

It has the particularity of having a Royal Pantheon located at the foot of the church, with Romanesque mural painting and original capitals, all of which makes it a unique piece of the Romanesque world of the time.

The complex was built and enlarged during the 11th and 12th centuries.

Originally it was a monastery dedicated to San Pelayo, although it is assumed that a Roman temple was previously based on its foundations. With the transfer of the remains of San Isidoro, Bishop of Seville, Doctor of Spain to León, the ownership of the temple was changed.

The church building preserves some Romanesque vestiges of the first construction of Fernando I and Sancha. The Pantheon and the two doors on its southern façade, called Puerta del Cordero and Puerta del Perdón, plus the North or Capitular Door, are the first manifestations of Romanesque art in the Leonese territories. Over time Gothic, Renaissance and Baroque modifications and additions were made.

The church and monastery of what is now known as the Basilica of San Isidoro had its origins around the year 956, a site next to the Roman wall of Legio VII Gemina, on the northwestern side. The entire western part of the building is attached and superimposed on it. Many meters of this fortress are preserved in good condition along this northwestern corner.

It has also been possible to detect under the buildings of the Collegiate Church, and after the restoration works, important Roman vestiges: thick brick walls, sewers, ceramics, tegulas, latrine culverts (conduit through which the waters of the house go to the drain) , with the seal of Legio VII.

Not a remnant of the Visigothic period remains, and neither does the Arab period, nor the early days of the Reconquest.

The first references in chronicles and documents appear in the middle of the 10th century, giving news of the churches of San Juan and San Pelayo, which around this time begin to develop.

King Sancho I of León (Sancho el Crasso) wanted this church to be built.

Throughout the centuries and up to the 21st century, it transformed itself physically and spiritually, suffering times of great splendor and times of authentic decadence. Here are the different phases it went through; These are phases with a lot of historical charge in which the influence of successive kings and their family environment was greatly noted.