Plaça Nova and the towers of Barcino

In front of you is one of the gates of Roman Barcelona. The two round towers on either side of Carrer del Bisbe protected the north-western entrance to Barcino, the small colony founded under the emperor Augustus, around 15 BC.

1A wall you can see, and one you can't

The first wall was a modest affair. Towards the end of the 3rd century and the start of the 4th, a time of insecurity across the Empire, it was replaced by a far stronger circuit, about 1,300 metres long and studded with dozens of towers. The ones you see were rebuilt and altered in the Middle Ages, but their base is Roman. On your left, beside the tower, a stretch of the arches of the aqueduct that brought water into town has been reconstructed: at a glance you can picture how people entered Barcino.

The iron letters spelling «Barcino» are a piece by the visual poet Joan Brossa, installed in the 1990s: a nod to the city's Latin name, right at the foot of its ancient wall.

2Picasso on the façade

Now turn to the concrete building of the College of Architects of Catalonia, designed by Xavier Busquets. Its friezes, unveiled in 1962, were made from drawings by Pablo Picasso: the Norwegian artist Carl Nesjar etched them into the concrete with a sandblaster. They are among Picasso's very few open-air works in the city where he trained as an artist.

Two thousand years separate the Roman stone from the etched concrete, and only a few metres of pavement.

3What to look for

• The two towers: notice the large blocks at the base, older than the upper sections.
• The aqueduct arches, rebuilt next to the left-hand tower.
• Picasso's frieze: children, giants and banners, as if at a street festival.