Until the 80s the consuls were military commanders first and foremost, and spent almost all of their time outside the city. This can be seen in lots of the circumstances surrounding the office. For example, the revision of the calendar by shifting the beginning of consular office by adding two extra months before March may be in part a political gesture, to extend the brief time that consuls spent in the city between taking office (originally March 15, then January 1) and going off on campaign. Consular office did not have an age limit until the lex Villia in 180, and extraordinarily young consuls were occasionally elected (e.g. Scipio). But the norm was for consuls to be, shall we say, mature leaders. This, combined with the military aspect of the consulship, made it virtually certain that some consuls--and other magistrates, naturally--were likely to die in office eventually.

In consulship was a particularly knotty problem in that the consuls were the possessors of the auspices, and by religious custom these had to be passed on in an unbroken sequence. Consuls presided over the elections of their successors, and at the end of the year the former consuls laid down the auspices, which were taken up by their successors. Moreover, the auspices were required for the holding of consular elections to begin with. The death of a sitting consul therefore raised not only political and procedural problems, but religious ones as well. In ordinary cases, with the death of a single consul, the surviving consul assumed his auspices and presided over the special election (for which the consul's own auspices would suffice) of a suffect consul, who would take the deceased's position for the remainder of the year. This could cause some issues, such as the need for the surviving consul to return from campaign to elect a suffect, but usually it wasn't too big a deal. In the unfortunate event that both consuls were either killed or incapacitated, which did happen sometimes, the auspices were assumed by an interrex. The interrex, one of the handful of magistracies still exclusive to patricians by the historical period, had no colleague and was, almost uniquely, chosen by the senate from is own ranks, to which he returned after the completion of his duties. The interrex had five days to take the auspices and hold consular elections. If the auspices were bad and forbade the elections, or for some other reason he was unable to complete the elections, after five days the interrex named a successor, who likewise held the position for five days, and so on until the consular elections were held. Normally this action was carried out in an orderly fashion, and only when neither consul could preside over the elections. Towards the end of the Republic this could be an issue, however, as elections frequently became postponed to mere days before the assumption of office and turmoil disrupted normal political procedure. Interreges presided over the elections of Crassus and Pompey for the consulship of 54, and interreges presided over the elections in 53 and 52 as well. Prior to Sulla (elected to the dictatorship with an interrex presiding) interreges had not been appointed since the late third century, after which point consular elections that could not be carried out by either consul were usually handled by briefly-serving dictators who handled the auspices. The last interregnum, in 52, was caused by the rioting that occurred after Clodius' murder by Milo, which prevented the elections from occurring. After fifteen interreges eventually Pompey was made sole consul without election.

This last case is not unimportant, because the conditions under which suffect consuls were supposed to be elected were not always entirely clear. The death of a consul was obvious enough. The death of both consuls clearly necessitated some sort of special action to preserve the auspices, whether interregnum or the appointment of a dictator to preside over the elections--of course, in the most famous example of such a calamity, Octavian assumed an extraordinary magistracy immediately after the deaths of both consuls, Hirtius and Pansa, at Mutina, without resorting to either measure (the dictatorship had been outlawed by Antony recently anyway). But what if a consul was simply no longer a consul? This problem arose in 87, when Cinna was driven from the city and deprived of his consulship by senatorial decree. Under normal circumstances consular office could be revoked, but only by a vote of the people in the centuriate assembly, which was to elect a new consul to replace him. Cinna, Appian tells us, went to the army at Nola (which was not his army, but App. Claudius's, which sort of seems to sink any argument for "client armies" as the cause for civil warfare in the first century) and appealed to them, stating that they, as citizens, had granted him consular office (a common oratorical formula) and that only they had the right to take it away. The senate's actions were therefore, Appian's Cinna says, not only an insult to him but a direct assault on the power of the people to elect the magistrates. The appeal to an army particularly was more than practical, it was symbolic: the consul, as a traditionally military leader, was elected by the centuriate assembly, symbolically the Roman people in their guise as a citizen militia electing its own leaders. Cinna's further argument, that the senate by this move would (if it was allowed to stand as a precedent) legitimize the ignoring of the voting assemblies and take the state for themselves, was clearly effective, and probably was quite a real fear. The language of the texts is somewhat unclear. Appian says the senate (singular, βουλή) outlawed Cinna and that they (ἐχειροτόνησαν, plural) elected Merula as suffect consul. The switch from singular to plural might be Plutarch's expansion of the senate to the body of individual senators (particularly appropriate in an electoral context) or it might be Plutarch switching the subject to the Roman people, who are not explicitly mentioned. Likewise, the verb might mean that the senate itself elected him or that an election (presumably a normal one) was held. It's hard to say--depending on what we think, the election of the suffect consul might have suffered a serious misuse.

In the Principate the suffect consulship gained a new character. The end of free elections (originally still held as a formality, but ultimately abolished entirely) and the primacy of the emperor made the consulship more a mark of formal prestige and imperial favor than anything else. Two consuls were still created (in many years, and often in succession, including the emperor himself), but in addition to these several sets of suffect consuls were created. Initially these pairs took up consular duties for four months each, but eventually this time narrowed to only one month: in some years honorary suffect consuls, who had no actual duties, were also named. Consuls might still die, of course--but in such circumstances not only did it not matter, but they could be replaced easily anyway!