File:Bust of Antoninus Pius 01.jpg

English: In the Loggia.

A Roman tradition, codified by the historian Suetonius in his imperial biographies, considered the twelve Roman emperors or "Caesars" the embodiment of all political and military virtues worthy of aspiration. Following the ancient example, it became common in the Renaissance to include a complete series of busts of the Twelve Caesars in a private collection of antiquities. They were usually displayed in the gardens of villas, in loggias, or in the galleries of private palaces. Some families succeeded in acquiring more than one set of these portraits. The Ludovisis family possessed two complete series of the Twelve Caesars, The most valuable among the two was sold in 1669 to Ferdinando II, Grand Duke of Tuscany, and is now on display in the Uffizi Gallery in Florence. The second series, displayed here, is composed of some busts acquired in 1622 from the Cesi Collection, which had previously belonged to the Altemps Collection, and some others from the Villa Altemps in Frascati, acquired by Cardinal Ludovisi in 1621. Of the twelve busts displayed in the Painted Loggia, only eight are deemed to be probably representing Roman emperors. To these have been added - in order to complete the canonical series of twelve portraits - two unidentified bearded heads and two Roman busts of the poet Menander in order to complete the canonical series of 12 portraits.

Among the imperial busts are, all of which are heavily reworked in modern times, two are particularly noteworthy for their superior workmanship, namely the portraits of Hadrian and Septimius Severus.