Consideration of Tetrarchic portraiture has usually focused on the extant porphyry sculptures (plates 2, 6, 7, 9, and 10). This was perhaps inevitable, since the arresting eyes of the Cairo bust or the stubby legs of the Vatican groups are certainly curious. Few scholars have resisted the temptation to pronounce their aesthetic judgement (and why not?), but none has been as caustic as Bernard Berenson who saw in them ‘the meanest symptoms of decay’, an effect into which the sculptor had ‘simply blundered and stumbled’. Berenson's book and many of the other academic works which refer to the porphyry sculptures address the wider issue of style and, in particular, stylistic change in Late Antiquity. They cite the same art, but draw a range of conclusions: L'Orange proposes parallels between style and the structure of society; Kitzinger suggests a conscious approximation to a ‘sub-antique’ style; and Bandinelli sees the porphyry work as exceptional, specialized and short-lived. Without neglecting the porphyry sculpture, the present essay aims to consider the whole range of surviving portraits and to make sense of them within the relatively narrow field of Tetrarchic ideology. This necessarily involves the question of style and, therefore, has points of contact with the above ideas. However, the present study is primarily ‘internal’, drawing together images diverse in form and location. Patterns are soon apparent, but the Tetrarchy had to establish its ideological stability and credibility if the government were to endure. It collapsed quickly (A.D. 284–311), but in this respect, Tetrarchic portraiture offers a good example of the power of art to manipulate its audience by instilling belief.