Seemingly wedged between the cathedral and the remains of Barcino’s Roman walls, this stately square serves as the front porch of the 11th-century Palau Reial Major, palace of the kings of Aragón and Catalunya, and its related complex of buildings, including the Museu Frederic Marès (above). The chief attraction here is the guided tour of underground walkways over the excavations of Barcino, the city founded by the Romans in the 1st century b.c. and ruled by the Visigoths until the Moors leveled it in the 8th century a.d. The tour is offered by the Museu d’Història de la Ciutat. Although they are partially visible from Plaça del Rei, the last remaining Roman walls and defensive towers of Barcino—a section from the 4th-century a.d. second enclosure—are easier to make out from the opposite side, on Plaça Ramon Berenguer on Via Laietana. Embedded within the wall are the royal chapel of Santa Ágata and a 14th-century segment of the Palau Reial.