The two annually elected consuls were the most important of these, each of whom normally received an army and a specific enemy to campaign against as soon as he entered office. The praetors were junior commanders who usually received smaller armies and less important commands, or one might be kept in the city during his year in office to defend the city or attend to other matters. There were two praetors during the First Punic War, but the creation of an additional pair in 227 BC brought the total to four during the Second Punic War. Dictators were extraordinary commanders that could be created to face emergencies or perform necessary duties, usually in place of absent consuls. Finally, when the Romans felt it appropriate or necessary to keep a consul or praetor in the field beyond the expiration of his term in office, they could prorogue him in his command, which meant he retained his military authority (imperium) even after his magistracy and civilian authority (potestas) lapsed. Such men became proconsuls or propraetors, the titles signifying that they were no longer magistrates and were operating ‘in place of’ a consul or praetor.
Imperium
While the Romans had this range of different types of military commanders, in the Republic they had only one type of military authority: . Dictators, consuls, praetors, proconsuls, and propraetors all received by a law of the people (a ), and so each was a fully authorized and independent commander: each was a commander-in-chief. Modern historians, raised in a time when ranks and chains of command are universal foundations of military organization, often assume that must have existed in different levels or degrees, so that dictators had greater () than consuls, while praetors had lower () than consuls. Yet no evidence for such a division of exists until the last decades of the Republic. Quite the opposite: the Romans clearly believed that was a single, absolute, and indivisible idea, and that it conveyed the absolute authority to give orders and compel obedience from Roman citizen-soldiers. The completeness of came from its supposed origin: the Romans believed that it had been the absolute authority of their legendary kings, which had been transferred to the two consuls at the foundation of the Republic. Thus they believed the of the consuls was the supreme and complete authority of a monarch; it conferred total and unchallenged
