The cathedral was constructed over the crypt of a former Visigothic chapel, dedicated to Saint James, which was the proprietary church of the Viscounts of Barcelona, one of whom, Mir Gerberto, sold it in 1058 to bishop Guisleberto. Its site faced the Roman forum of Barcelona,
It is a hall church, vaulted over five aisles, the outer two divided into chapels. The transept is truncated. The east end is a chevet of nine radiating chapels connected by an ambulatory. The high altar is raised, allowing a clear view into the crypt.
The cathedral is dedicated to Eulalia of Barcelona, co-patron saint of Barcelona, a young virgin who, according to Catholic tradition, suffered martyrdom during Roman times in Barcelona. One story is that she was exposed naked in the public square and a miraculous snowfall in mid-spring covered her nudity. The enraged Romans put her into a barrel with knives stuck into it and rolled it down a street (according to tradition, the one now called 'Baixada de Santa Eulalia'). The body of Saint Eulalia is entombed in the cathedral's crypt.