Oriolo Romano is an example of a small 16th-century town built according to a rational and functional layout by Giorgio Santacroce. He invited farmers and peasants from Umbria and Tuscany to clear and plow the land and provided housing for them. Even nowadays, the inhabitants of Oriolo still use idioms and expressions that hail back to their ancestors' original homelands.

Santacroce’s work is celebrated by an inscription on the main building in Oriolo, the Renaissance building known as Villa Altieri. The structure was named after the family who became lords of Oriolo in the late 17th century. The family even produced a pope, Clement X.

Palazzo Altieri is an excellent example of Mannerist architecture applied to the fortified mansions owned by Rome's noble families. Some claim it’s the brainchild of 16th-century Italian architect Il Vignola, but it’s likely less famous architects were responsible for its construction. Work on the building was completed by Carlo Fontana in the late 17th century.

Today, visitors can explore 14 rooms, most of which are decorated with beautiful frescoes believed to be from the school of Taddeo Zuccari. Among other noteworthy details are the late 18th-century dining hall with its views of the Altieri fiefdoms and a collection of paintings by Jacob-Ferdinand Voet.

The Palazzo's claim to fame is that it houses an incredibly complete gallery full of portraits of the popes, from Saint Peter to Pope Francis. The collection presents each pope's portrait with a heraldic symbol, a description in Latin of the pope's deeds, and a motto. The portraits in Oriolo were used as a source to reconstruct the collection in Saint Paul's Basilica, which was partly destroyed by a great fire in 1823.