The Palazzo Altemps is located in the modern rione Ponte, part of the Campus Martius, and directly north of the Piazza Navona. In the ancient Rome, this site was only 160 meters from the Ponte Elio, and was one of the two main marble ports on the Tiber River in Rome. The other was located in what is now Testaccio. In 1891, during the construction works to build the embankments that now hold back the Tiber River, the remains of this dock were uncovered. The marble was worked—into statuary, sculptural decoration, or architectural decoration— in shops, the ruins of which have been found in the zone between the church of Sant’Andrea della Valle, the Chiesa Nuova, and the Tiber River. A few of these ancient shops bear signs of hasty abandonment after the time of the emperor Trajan; tools and even unfinished statues were discovered in some cases. There was also likely a temple to Apollo located in this area, over which has been built the church of Sant’Apollinare.

In the Middle Ages and onwards, the Campus Martius was divided between by the Ghibelline eastern zone, led by the aristocratic Colonna family, and a western zone by the Guelfs, led by the Orsini family. The division was mostly abandoned after the Great Schism in the 15th century, and the Campus Martius underwent a period of urbanization, leading to the present Palazzo Altemps.
The building was designed in the 15th century by Melozzo da Forlì for Girolamo Riario, who was related to Pope Sixtus IV. There is still a fresco on one wall of the Room of the Sideboard in the Palazzo that celebrates the wedding of Girolamo to Caterina Sforza in 1477, showing the silver plates and other wedding gifts given to the couple. When the Riario family began to decline after the death of Pope Sixtus IV, the Palazzo was sold to Cardinal Francesco Soderini of Volterra, who commissioned further refinements from the architects Sangallo the Elder and Baldassarre Peruzzi.
When the Soderini family fell on hard times, he in turn sold it in 1568 to the Austrian-born cardinal Mark Sittich von Hohenems Altemps, the son of the sister of Pope Pius IV. Cardinal Altemps commissioned the architect Martino Longhi to expand and improve the palazzo; it was Longhi who built the belvedere. Cardinal Altemps accumulated an impressive collection of books and ancient sculpture. Though his position as the second son in his family meant Marco Sittico Altemps became a cleric, he was not inclined to priesthood. His mistress bore him a son, Roberto, made Duke of Gallese. Unfortunately, Roberto Altemps did not enjoy the Palace long; he was executed for adultery in 1586 by Pope Sixtus V. The Altemps family continued, though, to mix in the circles of Italian nobility throughout the 17th century. Roberto’s granddaughter Maria Cristina d’Altemps married Ippolito Lante Montefeltro della Rovere, Duke of Bomarzo. The Palazzo Altemps became the property of the Holy See in the 19th century, and the building was used as a seminary for a short time. It was granted to the Italian State in 1982 and after 15 years of restoration, inaugurated as a museum in 1997.
It houses the museum’s displays on the history of collecting (sculptures from Renaissance collections such as the Boncompagni-Ludovisi and Mattei collections, including the Ludovisi Ares, Ludovisi Throne, and the Suicide of a Gaul (from the same Pergamon group as the Dying Gaul) and the Egyptian Collection (sculptures of eastern deities). The palace also includes the historic private theatre, at present used to house temporary exhibitions, and the church of Sant’ Aniceto.