The core of the museum was then centered on the archaeological remains of the Roman and late antique city together with the medieval royal palace in Plaça del Rei (Palau Reial Major), which includes the main hall called Saló del Tinell (14th century) and the palatine chapel dedicated to Saint Agatha (14th century) with its 15th-century Gothic altarpiece, a work of the medieval painter Jaume Huguet.

Several rooms of the rebuilt Casa Padellàs also exhibited objects bearing witness to the history of Barcelona along late medieval and modern times, up to the early 20th Century: the city government and its regulations, the guilds, civic celebrations, wars and conflicts, crafts and trade, the International Expositions held in Barcelona and the growth and transformation of the city in the industrial era, among other topics.

The museum gradually incorporated new sites such as the Temple of Augustus and the Roman sepulchral way in Vila de Madrid square (found in 1954).

Since 1996 Casa Padellàs's rooms serve for temporary exhibitions that allow more dynamic overviews and crossed discussions about key subjects of Barcelona's history.

Others refer to medieval times and the rest cover the contemporary city, including old industrial buildings and sites related to Gaudí and the Spanish Civil War.