Apart from 4,000 m2 of archaeological remains below the square, the monumental ensemble comprises the 11th-century Palau Comtal – the Count's Palace – later to become the Palau Reial Major – the residence of the kings of Catalonia and Aragon –, highlights of which include the Saló del Tinell, or Great Hall, and the 14th-century Chapel of Santa Àgata. The Watchtower of King Martí was added in the 16th century. The Casa Padellàs, a Gothic Renaissance palazzo which was moved to the Plaça del Rei at the beginning of the 20th century, completes the architectural ensemble.

The museum collections mainly comprise objects taken from archaeological digs and feature such diverse materials and objects as ceramics, stone, epigraphs, glass, silver and gold, marble and stone sculptures, architectural elements, organic materials, coins, etc... spanning the Neolithic period to the late Middle Ages. Highlights include Roman busts, most of them from archaeological digs around the Roman walls; Roman and Hebrew inscriptions and ceramics (plates, bowls, oil bottles, jugs, water bowls, drinking vessels…). The museum also has a varied collection of objects from other sources.