In 39 CE, Caligula built a three-mile-long pontoon bridge in the Bay of Naples and rode back and forth over it in a procession lasting two days. Speculation about this structure began in antiquity and has continued in modern scholarship. One branch of the literature has seized upon Seneca’s comment that Caligula’s bridge procession was “an imitation of a mad and foreign and misproud king” (De Brev. Vit. 18.5). But which king? Some commentators argue for the Achaemenids Darius and Xerxes and situate the episode within Rome’s Greco-Persian wars tradition – a reading strengthened by Caligula’s use in the spectacle of another Darius, a recent hostage from the Parthian king (Suet. Calig. 19.3; Dio 59.17.5-11; Momigliano 1932; Hurley 1993: 77-8; Spawforth 1994: 238-42). Others latch onto the detail that Caligula wore the breastplate of Alexander the Great during the procession and see the emperor’s pageant as an instance of Alexandri imitatio, the imitation of Alexander (Dio 59.17.3; cf. Suet. Calig. 52; Balsdon 1934: 54; Edmonson 1992: 164; Malloch 2001).
What was the effect of evoking both the Achaemenids and the Macedonian king in a single event? In this paper, I argue that the Greco-Persian wars and Alexander were historical exempla that supported different and largely incompatible Roman policies in the Parthian east, and that the ambiguity of Caligula’s bridge procession perfectly encapsulated the ideological tension at Rome that sprung from these competing historical traditions.
The lesson the Romans drew from the Achaemenid invasion of Greece was that the desire to yoke east and west together was hubristic folly. The idea played a major role in the formulation of eastern policy during the early Principate. Augustan propaganda conflated the Parthians with the Achaemenids, the ancient masters of the Orient; by extension, the Romans identified themselves with the classical Greeks, the defenders of Europe against eastern invaders (Sonnabend 1986: 273-88; Spawforth 1994: 238; Shayegan 2011: 339). This reading of history helped institute what Justin (41.1.1) called the divisio orbis, the sharp division of the world between the Romans in the west and the Parthians in the east.
At the same time, the towering figure of Alexander the Great bolstered deeply ingrained Roman pretensions to world rule. Roman portraits of Alexander could be positive or negative, but his influence as a model for eastern conquerors left its mark on Roman commanders from Pompey to Caracalla and beyond (Heuss 1954; Vogt 1969: 303-8; Isager 1993; Kühnen 2008). Alexander did not sustain the division between east and west – he obliterated it. The empire of the Parthians had reestablished the ancient boundary along the Euphrates, but Roman arms might erase it again. The Alexandri imitatio offered a template for universal conquest, and many Roman leaders followed the Macedonian’s example.
Caligula’s bridge procession drew on imagery from both the Greco-Persian wars tradition and the Alexandri imitatio. The competing ideologies that these traditions sustained then clashed, to deleterious effect, within the confines of a single event. The emperor’s pageant simultaneously told two different stories with two different morals. The result, as I demonstrate, was the sort of spectacle that emerges from the ancient sources: bombastic, devoid of clear meaning, and the work of a ruler who was slowly slipping into madness.
The Figure of the Tyrant