It is no easy task to pin a name on an ancient image of an early Roman emperor and make it stick. In the absence of a pedestal or inscription, a face may be identified by turning to two important guides. In his Lives of the Caesars, the antiquarian Suetonius (AD 69–122) describes the appearances of Julius Caesar and the eleven emperors up to Domitian who followed him. These thumbnail sketches can then be complemented by the miniature portraits stamped on ancient Roman coins. Even when using these resources, the judgements are rarely uncontested. Take, for example, the case of the Grimani Vitellius. Bequeathed to Venice by Cardinal Domenico Grimani on his death in 1523, this ancient marble bust was identified as depicting Emperor Vitellius, who reigned for most of AD 69, on the basis of a ‘match’ with the numismatic evidence. (It will surprise many to learn that this bust is ‘perhaps the most recognisable and replicated of all imperial portraits’, with a starring role even in 19th-century phrenology.) Recently, however, the Grimani Vitellius has been demoted to Grimani Ignotus: rather disappointingly, the bust is now thought to depict an unknown Roman of the second century AD.

The writings of Suetonius and the portraits on ancient coins have served as the chief inspiration for images of Roman emperors in Western art since the Renaissance. In Twelve Caesars, the beautifully illustrated book based on her 2011 A W Mellon Lectures in the Fine Arts and the