The unlimited _imperium_ of the consul in the field (_militiae_), which was asserted when he had crossed the _pomerium_[902] and required the sanction of the _lex curiata_, was, in the early Republic when wars were confined to Italy, generally exercised by both the consuls together. To avoid the inconvenience and danger attending the rule of two commanders-in-chief of equal power, the principle of rotation was adopted, each consul having the supreme command for a single day.[903] But this device was necessary only when military considerations dictated that all the Roman forces should act together. Frequently the Roman armies had been simultaneously directed against various points of Italy, and the custom naturally suggested itself that each consul should command half of the regular army of four legions, and thus have an independent sphere of operations (_provincia_).[904] In a defensive war, such as that against Hannibal, Italy would naturally fall into two consular provinces;[905] but the practice became even more essential when the Roman arms extended beyond the peninsula, and in the period of the acquisition of the empire, from the beginning of the first Punic war to the close of the struggle with Greece (264-146 B.C.), _Italia_ as a whole, and some foreign country such as Greece or Macedon, are the regular _provinciae_ held by the consuls.[906] The arrangements which were made for the permanent government of provinces, first through praetors and afterwards through pro-magistrates, tended to arrest their employment for this purpose; but down to the time of Sulla (81 B.C.) a consul might at any time be appointed to a transmarine province.[907]