Palazzo Spada is a magnificent, yet lesser-known, palace located in the Regola district of Rome in the city's historic center. It features an extraordinary art collection (Galleria Spada) which showcases works by the likes of Guido Reni, Titian, Guercino, Rubens, Caravaggio, and Artemisia Gentileschi to name a few.

The collection was assembled by the two brothers, Cardinal Bernardino and Virginio of the Spada family during the 17th-century. As visitors enter the building, they are greeted by the extraordinary Mannerist stucco façade, complete with elaborate and flamboyant decorative elements.

Upon purchasing the building, Bernardino obtained the services of the famous architect Francesco Borromini who introduced a series of modifications, including one of his most remarkable creations: a massive optical illusion.

The optical illusion is located in the Palazzo's courtyard and consists of a colonnaded gallery dating to the 17th-century. The colonnaded leads to a heroic statue of Mars. However, what Borromini really created was a perspective gallery. The corridor is much shorter and the sculpture much smaller than they actually appear. The hall is only 26 feet (8 meters) long and the statue is only 24 inches (60 centimeters) high.

Borromini's extraordinary mastery of mathematics also reveals his perfectionism and neurotic nature. Borromini was also aided by an Agonistinian monk, Giovanni Maria da Bitonto, who was an expert in the accelerated perspective technique.