When the Emperor Augustus died in AD 14, the people of Tarraco asked permission to build a temple to him, and Tiberius agreed. Tacitus records the request, and the rhetorician Quintilian preserves a joke from the emperor's lifetime: when the people of Tarraco reported that a palm tree had sprouted on his altar, Augustus replied that it showed how seldom they lit the fire on it. The imperial cult enclosure, the sacred precinct of the provincial capital, occupied the top of the hill, and what survives of it now lies under and beside the cathedral of Tarragona.
The idea was to bring the provinces together in worship of the emperor, which meant that every year delegates from across the province gathered here, to honour Rome and, not incidentally, to discuss local politics. A great terrace was built on the heights, with a temple and a surrounding portico, and the result was one of the most visible symbols of imperial power in the Spanish provinces. Fragments of the precinct wall can be seen in the cathedral cloister and in the old town, and the whole area belongs to the Roman Tarraco ensemble listed by UNESCO in 2000.
The cathedral itself is a fine Romanesque and Gothic building, begun in the twelfth century on the same hill, and its cloister has carved capitals worth a slow look. The street plan of the old town follows in part the lines of the Roman streets, and walking the lanes you will cross from one era to the next several times in a minute.
Tarragona is a city of about a hundred and forty thousand people, with fuel and every service, and the easiest approach is by the coast or by the motorway from Barcelona. Inland, the roads wind through vineyards and hills, and the Mas de Torres, which shares the ride, is a countryside stop. The old town is hilly and paved with stone, so park in a garage and walk.
Aim for the morning, when the stone is cool and the light is clean, and avoid the heat of August afternoons.