The Museu Diocesà buildings include a section of the 4th century Roman walls and tower. It brings together a collection of more than 3,000 objects, including sculptures, paintings, silverware and goldware, ceramics and religious clothing. A series of exhibits spanning the Roman, Visigothic and medieval periods to the 21st century.

The institution began displaying its treasures in 1916 on the ground floor of the chaplains' seminary in the Eixample district. It has moved with the times and brought on board new artists, such as the sculptor Josep Plandiura, who created the Gaudiesque door on the front of the building in 1999.

The three-storey exhibition space also hosts temporary shows on a variety of themes highlighting the relationship between faith and culture. One of the highlights is the permanent exhibition entitled Barcino, Barchinona, Barcelona. A City, A Bishop, A Land.