Books and articles by the dozen refer to the Byzantine empire, and since Byzantium was in all periods ‘a significant other’ for the west (Arnason 2010: 503), it is appropriate to ask what kind of state it actually was. The question is timely since, albeit with some notable exceptions, Byzantium has played a lesser role than the Roman empire has in the extensive and growing study of empires (Alcock et al. (eds.) 2001; Cline and Graham (eds.) 2011; Bang and Bayly (eds.) 2011). Older publications evaluated this empire in very different ways, as ‘theocratic’, ‘totalitarian’, or, conversely, multicultural and universal (Runciman 1977; Kazhdan and Constable 1982; Laiou and Maguire (eds.) 1992), but all took Byzantium’s imperial status for granted. The very idea of Byzantium conferred a level of hegemonial status in the medieval world, independently of its actual organization as a state. Moreover, Byzantium’s reach extended beyond its borders: cultures and practices outside the Byzantine empire, for instance in the Islamic east, can also reasonably be seen as Byzantine. Yet the very contrast in state formation between Byzantium and the medieval west (Haldon 2015a) and Byzantium’s traditionally imperial identification make it important to consider how well Byzantium fits the context of the currently lively debate about empires.