2. The dread _imperium_ was now not only limited in the period of its tenure, but the possibility of an arbitrary use of it was averted in two ways. First, the two consuls had a veto on each other’s action, and both at home and in the field they took it in turn to exercise the _imperium_. Secondly, they could not put a citizen to death in the city unless the people in their assembly sanctioned it; in the field the Romans wisely left the _imperium_ unlimited, feeling, as we still feel, that military discipline needs a more forceful sanction than civil. And besides these two restrictions, the council of elders, the Senate, was retained to act as a general advising body for the consuls, who, however, themselves had the power of filling up vacancies in it from time to time. We do not know exactly what its composition was at this time; but it is certain that all who had held the _imperium_ had seats in it, as men whose service and experience best entitled them to advise and criticise their successors. This principle, that ex-magistrates should be members of the Senate, was adhered to at all times, and eventually made this great council into the most effective assembly of men of capacity and experience in practical life that the world has ever seen. Before we leave the _imperium_, for the present, one interesting fact must be noted. The Romans were not afraid to withdraw for a time these restrictions on the magistrate’s power, and to revert to absolute government, if they thought it necessary for the safety of the State. In moments of great peril, civil or military, the consul, on the advice of the Senate, would appoint a single individual to hold office for a fixed time with unlimited _imperium_; and in this case the assembly was not called on even to ratify the choice, so great was the trust reposed in the Fathers of the State. They did not call this single magistrate by the hated name of Rex, but used another word well known in Latium, Dictator. The institution was of the utmost value to a people constantly in a state of struggle and endeavour, and shows well the practical sagacity which a long training in duty and discipline had already developed.