The fleets are often neglected in consideration of the military forces of the Roman empire – indeed, some estimates of military strength have ignored them completely.1 Even more egregious is their omission in discussions of the rôle of the army in disseminating Roman citizenship, since the soldiers serving in the fleets benefitted from the same system of regular grants as did auxiliaries. When the fleets are included in inventories of the military, most scholars reckon them at either 30,000 or 40,000 men. In so doing, they are relying explicitly or implicitly on the work of C. G. Starr or M. Reddé, respectively. There has been no discussion of the discrepancy between them. Moreover, those who rely on Reddé tend to overlook the fact that he himself implied a strength of more than 50,000 men. This paper aims to draw attention to the significance of the large divergence between the two estimates and to offer a new one that takes better account of the uncertainties involved. It reviews the evidence adduced by Starr and Reddé but also draws on newer data from the archaeology of fleet bases and military diplomas. I conclude that the combined strength of the fleets was probably c.25,000 men, somewhat smaller than Starr suggested. Yet it is just as important to recognise that the margin of error remains large.