We wished to validate a very general agent-based model we had built concerning the rise of hegemony in different domains of international relations (https://doi.org/10.1155/2018/9306128). Our model focussed on the new domain of cyberspace, where the data are thin and the time series short. But with parameter changes it also spoke to the land, sea, air and space domains. So we sought validation in a time series from the land domain where the data are richer and the time series longer. We wished to compare the model’s results – the emergence, power accumulation, and behaviour of hegemons vis-à-vis the power accumulation and behaviour of the remainder of the international order – to empirically observed historical hegemonic behaviour. To this end, we built an exhaustive and novel database of the Roman Empire’s accumulation and application of power – represented by the proxy of military power in terms of force size and deployment – over the seven centuries of Rome’s undoubted hegemony. This historical record comfortably validates the main results of the model.