The Santa Iglesia Catedral Basílica Metropolitana de la Santa Cruz y Santa Eulalia - also known as the Seo instead of the cathedral - is Barcelona's Gothic cathedral.

The present cathedral was built during the 13th to 15th centuries on top of the old Romanesque cathedral, itself built on top of a church from the Visigothic period, which was preceded by an early Christian basilica, the remains of which can be seen underground in the City History Museum.

The completion of the imposing façade in the same style, however, is much more modern (19th century).

It has been dedicated to the Holy Cross since 599 and was added from 877 onwards to Saint Eulalia, patron saint of the city of Barcelona, a young maiden who, according to Catholic tradition, suffered martyrdom during Roman times. One such story has it that she was exposed naked in the city's forum and that miraculously, in mid-spring, a snowfall covered her nudity. The enraged Roman authorities put her in a barrel with broken glass, nails and knives stuck in it and threw the barrel down the hill. And so on, up to thirteen different martyrdoms, one for each year of the saint's age. Finally, she was crucified on a cross in the shape of a cross-shape, which is the emblem of the cathedral and the diocese, as well as the iconographic attribute of the saint.

Like most Gothic cathedrals, Barcelona's cathedral also has gargoyles, through which rainwater is poured from the roofs. They represent fantastic animals, such as lions, unicorns and one of the most famous is the one representing an elephant. The oldest ones are those in the part of the apse next to the door of St. Ivo dating from the early 14th century. The gargoyles in the cloister date from the 15th century, and the gargoyles in the four corners represent the symbols of the Evangelists.

According to popular belief, on Fridays it was bad luck to clash two or more keys; when the cathedral had to be closed, it was announced precisely by the noise caused by the clashing of keys, except on Fridays when a bell was rung and the altar boys carried the keys, one in each hand.