Construction of the third cathedral, now Gothic in style, began circa 1205, but problems with the foundation delayed continued work until 1255 under Bishop Martín Fernández with the support of King Alfonso X of Castile and León.
The design is attributed to the master Enrique, perhaps a native of France, who had previously worked on the Cathedral of Burgos.
Clearly, he knew the Gothic architectural form of the Isle of France.
He died in 1277 and was replaced by the Spaniard Juan Perez.
In 1289, Bishop Martín Fernández was also dying when the front of the temple was already open for worship.
The basic structure of the cathedral was finished soon, and in 1302 Bishop Gonzalo Osorio opened the whole church to the faithful.
The cloister and the north tower were completed in the fourteenth century.
The south tower was not completed until the second half of the fifteenth century.

The Cathedral of Leon, like its sister predecessor, Burgos Cathedral, follows the layout of the Reims Cathedral.
Like most French cathedrals, the one of Leon is built with a geometric module based on the triangle (ad triangulum), the primary lines of which relate to the square root of 3, and to which respond all of the parts and the whole.
This aspect, as with the layout, the elevations, and the decorative and symbolic repertoires, makes this cathedral an authentic trans-Pyrenee building, removed from Hispanic fashion and belonging to the purest school of French Champagne.
This has earned it the epithets of being "the most French of Spanish cathedrals" or the Pulchra Leonina (the Beauty of Leon), since its formal features are related to the Gothic style of Champagne.

In addition to its layout, the Cathedral of Leon is also inspired by that of Rheims in its structure, the form of the chapels of its ambulatory (in this case polygonal), and the development of its transept.
The influence of Chartres Cathedral can be seen in the western porch.
The one in Leon abandons the model of Rheims Cathedral in the elevations beyond the body of the clerestory, as it is transparent there and it accommodates the technical progress achieved in the Sainte Chapelle and Amiens Cathedral.

French influence is also found in developing the chancel, where initially the choir was to be put according to their custom.
Specifically Leonese is the location of the cloister, with no organic tie to the temple, the exit in the floor plan of the towers of the main facade, displaying the elevation of the buttresses of the nave, and the discontinuity of the five naves at the front end of the main area of the temple, which were reduced to three.

The problem was that much of the foundation site sits upon Roman ruins, hypocausts of the second century, hampering a good foundation for the pillars.
The accumulation of moisture and water seepage caused serious inconveniences to the master builders.
Besides that, most of the stones of the cathedral are of poor quality rock, a limestone, with little resistance to atmospheric agents.
In addition, the subtlety of its style is a challenge to its construction materials; the numerous supports are extremely fragile, the lines are reduced to a total optimization, to such a degree that several architects of the time questioned whether such a project could remain standing.
This almost unreal structure, together with the poor quality of the stone and its poor foundation, forced it to suffer constant interventions and restorations from the fifteenth century on, changing the temple into a European model for transformative intervention, restoration and conservation.
Construction of the third cathedral, now Gothic in style, began circa 1205, but problems with the foundation delayed continued work until 1255 under Bishop Martín Fernández with the support of King Alfonso X of Castile and León. The design is attributed to the master Enrique, perhaps a native of France, who had previously worked on the Cathedral of Burgos. Clearly, he knew the Gothic architectural form of the Isle of France. He died in 1277 and was replaced by the Spaniard Juan Perez. In 1289, Bishop Martín Fernández was also dying when the front of the temple was already open for worship. The basic structure of the cathedral was finished soon, and in 1302 Bishop Gonzalo Osorio opened the whole church to the faithful. The cloister and the north tower were completed in the fourteenth century. The south tower was not completed until the second half of the fifteenth century. 
The Cathedral of Leon, like its sister predecessor, Burgos Cathedral, follows the layout of the Reims Cathedral. Like most French cathedrals, the one of Leon is built with a geometric module based on the triangle (ad triangulum), the primary lines of which relate to the square root of 3, and to which respond all of the parts and the whole. This aspect, as with the layout, the elevations, and the decorative and symbolic repertoires, makes this cathedral an authentic trans-Pyrenee building, removed from Hispanic fashion and belonging to the purest school of French Champagne. This has earned it the epithets of being "the most French of Spanish cathedrals" or the Pulchra Leonina (the Beauty of Leon), since its formal features are related to the Gothic style of Champagne. 
In addition to its layout, the Cathedral of Leon is also inspired by that of Rheims in its structure, the form of the chapels of its ambulatory (in this case polygonal), and the development of its transept. The influence of Chartres Cathedral can be seen in the western porch. The one in Leon abandons the model of Rheims Cathedral in the elevations beyond the body of the clerestory, as it is transparent there and it accommodates the technical progress achieved in the Sainte Chapelle and Amiens Cathedral.
French influence is also found in developing the chancel, where initially the choir was to be put according to their custom. Specifically Leonese is the location of the cloister, with no organic tie to the temple, the exit in the floor plan of the towers of the main facade, displaying the elevation of the buttresses of the nave, and the discontinuity of the five naves at the front end of the main area of the temple, which were reduced to three.
The problem was that much of the foundation site sits upon Roman ruins, hypocausts of the second century, hampering a good foundation for the pillars. The accumulation of moisture and water seepage caused serious inconveniences to the master builders. Besides that, most of the stones of the cathedral are of poor quality rock, a limestone, with little resistance to atmospheric agents. In addition, the subtlety of its style is a challenge to its construction materials; the numerous supports are extremely fragile, the lines are reduced to a total optimization, to such a degree that several architects of the time questioned whether such a project could remain standing. This almost unreal structure, together with the poor quality of the stone and its poor foundation, forced it to suffer constant interventions and restorations from the fifteenth century on, changing the temple into a European model for transformative intervention, restoration and conservation.
León Cathedral