The Cathedral of Barcelona is comprised of three naves, but just a single apse and ambulatory. The naves have five sections: that closest to the façade is the longest in order to accommodate the dimensions of the cimborio, which is adjacent to the main entrance.
The typical structure used in Catalan Gothic constructions, arranged to permit use of the spaces within the buttresses, allowed rows of secondary chapels to be opened up in the Cathedral. There are two chapels in each section of the naves, encircling the entire basilica.
Two large bell towers are located at the ends of the section nearest to the presbytery, with no side chapels. One of the towers is over the door of Saint lvo and the other is over the interior entryway to the Cloister. On the basilica's terraces, these towers are octagonal with a prismatic body used for the stairways, which are built into the towers (1386-1393 and 16th century).
Large windows open up onto the radial chapels of the ambulatory, illuminating the presbytery. In the lateral naves, a tall, windowed gallery runs above the chapels on the outer wall of the basilica. A small triforium runs around the central nave and the presbytery near the dome.