In the 2nd century B.C., a great wall was built around Tarraco, delimiting the municipal boundaries. The wall originally ran some 3,500 metres. Today, approximately 1,100 metres remain, bordering present-day Tarragona's Old Quarter. The walls are the oldest Roman construction still conserved outside Italy. Between the 16th and 18th centuries, they were reinforced with bulwarks, a curtain wall and exterior fortifications in order to adapt the Tarragona defences to new forms of artillery. 

The 'Passeig Arqueològic', or Archaeological Promenade, winds between the ancient Roman and modern curtain walls and is dotted with shaded gardens, romantic poetry and historical explanations. Special attention should be paid to the Archbishop's Tower, which underwent considerable alterations in the Middle Ages, and the Minerva Tower, which is the site of the oldest Roman sculpture and inscription in the Iberian Peninsula.