Promagistrate

In ancient Rome, a promagistrate (Latin: pro magistratu) was a person who was granted the power via prorogation to act in place of an ordinary magistrate in the field. This was normally pro consule or pro praetore, that is, in place of a consul or praetor, respectively. This was an expedient development, starting in 327 BC and becoming regular by 241 BC, that was meant to allow consuls and praetors to continue their activities in the field without disruption.

By allowing veteran commanders to stay in the field rather than being rotated out for someone who may not have had much experience in the theatre, the practice helped increase the chances of victory. Whether a commander, however, would be kept was largely decided politically and often motivated by commanders' ambitions. However, the effect of prorogation was to allow commanders to retain their positions as long as political support existed, weakening the republican check of the annual magistracy (and the rotation that implied) over commanders' activities.

Sometimes men who held no elected public office – that is, private citizens (privati) – were given imperium and prorogued, as justified by perceived military emergencies. This was most exemplified by Scipio Africanus and Pompey: the latter held a series of promagisterial commands before ever holding a magistracy or even joining the senate. With the expansion of the quaestiones perpetuae (permanent courts) in the late republic, it became normal for the provincial governors not to be one of the annual praetors: instead, an urban magistrate would be assigned a province after serving his urban term and prorogued.

The titles "proconsul" and "propraetor" are not used by Livy or literary sources of the republican era. Those Romans did not view a promagistracy as a formal office in the republic but rather as an administrative expedient. While during the middle republic it was common for praetors to be prorogued pro praetore and consuls pro consule, after the Sullan era essentially all promagistrates were pro consule, regardless of previous urban magistracy.