Qualities in other directions could more easily be ignored, but good generalship should be the monopoly of the Emperor.1
Tacitus puts this thought into Domitian’s mind in order to emphasize a dilemma confronting Roman emperors. They needed to employ competent commanders, but those commanders might be so militarily successful that they could challenge the emperor’s control of the army and undermine his political domination. In all ages and societies the interrelation of war and political structures has provoked debate among historians and social commentators. On one level, mass participation in war by a citizen militia can lead to political changes through the sacrifice and suffering of the ordinary citizens serving as soldiers, who vote in the assembly to bring about permanent changes in the constitution or extort temporary concessions from the governing group if their military contribution is considered essential. Therefore the ‘military participation rate’ can be a significant indicator of social and political change, and in some circumstances is perhaps relevant to the ancient world. On another level, one group in society can sometimes exploit a special or superior contribution in war to impose its rule on the rest of the population, or an individual can exploit his military leadership to stage a coup or buttress his faltering political authority. When military commanders compete for control within a state, it sometimes happens that ordinary soldiers acquire a political influence normally denied to them. Once in power, a leader might use his personal association with the army, his prowess in war and the promise of frequent war-making to change the pattern of government by establishing a purely military autocracy. Finally, the emergence of a professional army with a low level of military participation among the population as a whole might lead to domination by the soldiery in one form or another.2