2. The Constitution of the Empire
For a better understanding of the whole public law of the Roman empire, it is useful to recall the situation in the Mediterranean in the republican period.
The Mediterranean world at that time was a tapestry of independent city-states, each with its own written — or often unwritten — constitution, exercising its own foreign policy, having its own legislation, jurisdiction and administration, and imposing its own taxes on its citizens and residents. The major exception to this was Egypt, where the pharaoh was sole ruler, commander of the army, lawgiver, and judge. Rome was, originally, just another city-state with its own institutions. They were the senate, with advisory power (originally consisting of the heads of the patrician families, with the addition of former magistrates); the elected magistrates, with legislative and executive power (consuls, praetors, aediles, censors, dictator); and the people’s assemblies, with legislative power (the populus Romanus and the plebs). When larger entities began to be created, such as the Macedonian kingdom and its successor states, and the successor to all of these, the Roman empire, the existing constitutional structures were maintained. For Rome that meant that institutions designed for a city and its surrounding region now had to work for an ever-increasing and ultimately enormous area. By the first century BC it became clear that this was not possible. We do not know precisely what designs Julius Caesar had in mind. Perhaps it was indeed (as his detractors claimed) a monarchy modelled on the Hellenistic kings; that would have been better suited to a large territorial state than the republican constitution. But his murder made clear that that was very threatening to a large part of the Roman elite who wanted to keep the old system.Once Antony and Cleopatra had been defeated and the civil war had come to an end, Rome’s empire stretched all around the Mediterranean Sea, roughly bounded in the North by the Rhine and Danube, in the East by the Euphrates and Tigris, and in the South by the Sahara.
All territories had formally been subjected to the Roman people (meaning Rome, Italy, and certain colonies) as provinces. Only a few towns such as Marseilles were, as civitates liberae et foederatae, formally on a par with Rome. The provinces were governed by former magistrates of Rome, appointed by the Roman senate. The situation now became complicated. Formally, the republican institutions persisted, but they had been crafted for a city-state and were not fit for an empire such as this.Reform was necessary. But Caesar’s adoptive son Octavian (later Augustus) was very conscious of the resistance to Caesar’s aspirations and, after he had removed all opposition by 27 BC, thought it wise to retain the republican constitution. He did so by modifying it to the extent that alongside the unwritten customary constitution was an unwritten addendum, which effectively transferred most legislative and judicial power and the command of the army to him and his designated successors (who would also adopt the name of Caesar). Certain formal decisions provided the basis for the constitutional position of the emperor. On 13 January 27 BC, in a session of the senate, Octavian laid down all his powers as triumvir. He was then awarded the title ‘Augustus’, and the provinces were divided between him and the senate. He was to govern seven provinces with legions; the other twelve were to be governed by senatorial appointees. Augustus also received proconsular power (imperium proconsulare) and the command of the army. In 23 BC the power of a tribune (tribunicia potestas) was awarded to him as well. Both titles implied the right to issue edicts. After 12 BC he became pontifex maximus too. These three attributes remained constant for every emperor that followed. In addition, in the early years of the empire, at the accession of each new emperor a statute was passed in which these powers were awarded to him.2 They included the power to do everything which was in the interest of the state (ex usu rei publicae), such as concluding treaties. One of these, the lex de imperio Vespasiani, is preserved.
Until AD 383 imperial titles still continued to mention tribunicia potestas and imperium proconsulare.At the beginning of the principate the emperor was still just one of several constitutional organs, alongside the assemblies of the Roman people (the comitia and the concilium plebis) and the senate, albeit his position was now one of overwhelming authority and power. This changed: in the first century both the comitia and concilium plebis disappeared, and by the end of the second century the senate was reduced to a formality. It remained so. In AD 330 Constantinople was made the second capital, with its own senate and functionaries, but that did not change the situation. Its members were co-opted from sons of senators; high functionaries also became members; and the emperors could always appoint senators. Emperors were by this time appointed by the army, and the senate formally confirmed the candidate who had proved himself superior to the others. All the provinces were now governed by governors, appointed by the emperor alone.
Diocletian (who ruled from AD 284—305) changed the constitution. The empire would now have two emperors, called Augusti, who would each govern half of the empire. Each would appoint a future successor, called Caesar, who would administer a part of his half and succeed him after a certain period. The empire was divided into a number of praetorian prefectures, each prefecture into dioceses, each diocese comprising a number of provinces. Diocletian more than doubled the number of provinces, to over a hundred. He further separated the military administration from the civil administration. Governors were now pure civil servants. Military commanders ultimately reported to magistri militum and magistri equitum, who in their turn reported to the emperor. The administration was subject to checks: one could appeal against decisions.
Diocletian’s creation of two Augusti and two Caesars did not last long.
As soon as AD 324 Constantine seized sole power. The other innovations, however, did remain. Prospective emperors still needed the support of an army, but we can also see that being related to a former emperor was a point in a candidate’s favour. We see the same pattern here as is found with the senate and town councillors: birth and family ties became strong factors. But by now the army offered opportunities for social climbing: Valentinian and Valens began as soldiers; still later, barbarian generals exercised great influence and occupied high office. By that time (mid-fourth century) the powers of the emperor had fused into a customary amalgam of legislative, judicial, and administrative power, and after AD 383 the references to tribunicia potestas and proconsular imperium were dropped. The transfer of power, now complete, became the core of the unwritten constitution, the emperor being sole lawgiver, supreme judge, supreme administrator, and army commander. The republican institutions survived in a merely formal sense, although in the west the senate remained, politically and economically, a formidable power block. When Theodosius died in AD 395, his two young sons were without difficulty accepted as emperors. From that time the dynastic principle was a constitutional and almost conclusive factor in succession to the empire. It can be seen in the marriage policy of the emperors and usurpers: Pulcheria, the sister of Theodosius II, married the general Marcian to legitimize him as the successor to her brother; the usurper Petronius Probus forced a daughter of Valentinian III to marry his son.3.