Neoclassical symmetry and references to Greco-Roman architecture characterize the building. It is structured on a longitudinal axis and it is divided into five sections - two roundabouts, like “little pantheons”, at the extremes, two galleries full of windows, and a large central body where the main façade is located with its outstanding giant colonnade. In his native Madrid, architect Juan de Villanueva, who designed the building, was quite familiar with the local visual idiom, which was integrated most successfully with the combination of reddish brick and grey granite creating the bichrome effect that is so typical of the city’s architecture. The walls of the building are decorated on the outside with medallions depicting some of the main artists featured in the collection and allegorical sculptures of the virtues, all added to the Villanueva Building around 1830.