Preserved in the subsoil of the Plaça del Rei are the remains of Barcino, the Colonia Iulia Augusta Faventia Paterna Barcino, which was the founding site of Barcelona. These remains correspond to buildings and streets built and modified between the 1st century BC and the 6th century AD, and they reflect the social, economic and ideological changes undergone by the inhabitants of the ancient city.

Barcino was a small Roman colony founded in the 1st century BC. Over four centuries it developed a solid economic structure. When more difficult times arrived, the reinforcement of its wall enabled it to survive the crises suffered by the Empire that founded it and for its pre-eminence to surpass, in the 5th century, that of Tarraco, the capital of the province.