Marcus Aurelius assumed the throne according to a previously agreed upon succession, at a time of relative peace and prosperity for Rome. Though native to Rome, his family was of Iberian (Spanish) origin; Aurelius himself was a Stoic, and given to deep philosophical thought. With his rise to power, continued security for both the Roman state and society seemed likely. His entire rule, however, was occupied by challenges that would characterize Roman dilemmas for the next two-and-a-half centuries.
Aurelius' first year as emperor (a rule shared with his adopted half-brother Lucius Verus until 169) was appropriate to his mindset of Stoicism. In 161, the Tiber River flooded, the Chatti raided, legions revolted in Britain, and the Parthians of Persia attacked, as they were unsatisfied with disadvantageous borders instituted during the reign of Emperor Hadrian (130s CE). Though the Parthians seized Armenia for a short while, Roman response came in 163-64. An army was sent east under Verus' nominal authority, but with the effective control of general Avidius Cassius. After putting the Syrian legions through rigorous re-training, he captured and burnt the Armenian capital Artaxarta, and defeated the Persians at Dura Europa on the Euphrates. Proceeding down the Tigris, he destroyed Seleucia and Ctesiphon, the latter a Parthian capital (165-6). A raid into Media beyond the Euphrates was the farthest eastern journey by Roman forces to date, and resulted in bringing western Mesopotamia into the fold as a Roman dependency. Aurelius, recognizing the need for strong eastern defenses after this war, gave Cassius supreme command of all forces from Egypt east.
Complete destruction of the Parthian threat was prevented, though. Roman units returning from battle zones brought with them a plague. Thousands of legionnaires died in the field, after which the disease spread to the cities of the Mediterranean basin, becoming "the most destructive plague in Roman history." It lasted nearly fifteen years, with an almost thirty percent mortality rate among victims. It created a manpower shortage not only in civilian sectors such as the economy, but in the military as well.
It was at just this time (165-66) that Germanic tribes began to come over the Danube River into Roman territory. Finding the Roman garrisons depleted due to the Persian campaigns and the Plague, the Germanic Marcomanni and Quadi were even able to move through the Balkans and descend upon northern Italy, reaching Aquileia. Not only raiding and withdrawing now, there were hints that they would try to settle in Roman territories. The ferocity of their attacks was a new phenomenon, and suggested that population build-up in Barbarian areas was pushing them.
Though facing military resource shortages, Marcus Aurelius was resolute in his response. Raising taxes, depleting coinage of silver content, and even selling off some of the crown jewels, he raised the necessary funds without borrowing. He then secured troops from all classes, including slaves and gladiators, and built new fortifications along the front. From 167 on, he fought on a nearly yearly basis on the border districts. After initial Roman losses, the Marcomanni were defeated in 171, while the Quadi were eliminated as a direct threat in 174. The Sarmatians were defeated the next year. Marcus' planned offensive across the Danube was prevented in 175, however, by insurrection. Avidius Cassius, with control over eastern armies, had himself proclaimed emperor based on a rumor of Aurelius' death. Though Marcus Aurelius successfully suppressed the revolt, it was not until 178 that he was able to pursue the Quadi over the Danube into Bohemia. He was planning to advance the Roman border east and north to the Carpathian Mountains and Bohemia when he became ill and died in 180.
Aurelius died with an heir, the first Emperor to do so since Vespasian. Commodius, however, was the opposite of his father. Devoted to enjoyment and life in a fantasy world of self-adoration and athletics, he began his reign by forming a treaty with the Germanic tribes that did not reflect his father's successes. Barbarian prisoners were returned, and Rome agreed to pay a subsidy to the tribes to keep them away. For the next twelve years, Commodius tried to enjoy himself as much as possible. Retiring from public life except for sporting events in which he competed, he allowed courtiers and favorites to run the government. Administration quickly diminished, with bureaucratic offices actually going for sale. In 192, when he tried to appear in public as both a gladiator and a consul, he was killed by members of the Praetorian Guard, the elite Palace guard. The Praetorian Prefect, Laetus, then selected as emperor Helvius Pertinax, who had been a close adviser to M. Aurelius. The Senate accepted the nomination. Pertinax began his reign in a serious tone, rehabilitating depleted royal finances, taking the title princeps as opposed to the more imposing imperator, and insisting on stricter terms of military service. The Praetorians tired of him quickly, though, and murdered him in 193. Beginning a process that only grew in the next decades, the guards chose a successor, who was not universally acclaimed. Various imperial legions proclaimed their own commanding generals as Emperor, and up to four claimants fought out the succession.
Finally, the able general Septimius Severus (r. 193-211) of Pannonia (the Balkans) was acclaimed by his legions and defeated other claimants. Arriving in Rome, he held Pertinax's funeral, and then abolished the Praetorian Guard as a separate, independent force, and now selected his personal guard from out of his own legion troops. From this date, guard service in the palace was no longer reserved to men of Italian birth. After fruitless wars against the Parthians, Septimius ruled from Palmyra (Syria) and Carthage (N. Africa). He and his son Caracalla (211-17) disregarded senatorial prerogatives, and equalized citizenship status of all free men in Roman lands. Army supporters consented to rule of ineffective Severi relatives through to 235.
Major geopolitical changes from the 220s exerted transformative stresses on the Roman system. The Iranian Parthians had maintained an uneasy status quo with Rome in Mesopotamia; in 226, the Sassanid dynasty took over. Reviving ancient Achaemenid territorial claims as far west as Palestine, they ignited constant war in Rome's East. Removal of legions from the Danubian and Rhine borders (limes) to fight the Sassanid threat allowed violent barbarian incursions to begin in the 230s. Beginning with marauding Marcomanni and Alamanni in North-Central Rhineland, by 254 upper Germany fell. By 259 the Franks had occupied Belgium, and from 268 they and Alammani raided unopposed in Gaul for 11 years, interrupting agriculture, city life, and Imperial army supply as far as Iberia (Spain). Alamanni thrusts into N. Italy also occurred. Mauretenian tribal pressure in N. Africa was accompanied by havoc on the Danube limes. Sarmatians and Visigoths (Western Goths) attacked all along the Thracian and Moesian (Balkan) borders during the 250s and 260s, while Ostrogoths (Eastern Goths) advanced from the Crimea to ravage northern Asia Minor, and continued into the Bosphorous region and to the Aegean coast. Farmland was desolated, inland cities shrank, and government income curtailed. Barbarians began to relocate within Roman territory.
Responding to the challenge was a succession of generals of peasant stock from Illyricum and Pannonia (the Balkans and Danube frontier), each elevated by their legions and ruling for a while until assassinated by rival generals. Maximinus Thrace (r. 235-238; of Gothic-Alan background) resisted Sassanid and Marcomanni forces. The child-emperor Gordian III was murdered by the Prefect of the Praetorian Guard (Palace Guard, 244). Valerian (r. 253-260) fought holding actions against the Goths, Quadi, and Sarmatians, and was taken captive in battle against the Sassanids, dying in the East. Gallienus (d. 268) reformed the army, establishing reserves and rapid-reaction cavalry, while Claudius II Gothicus scored major victories against Alamanni and Goths (268- 269). Aurelian (270-75) defeated break-away generals (Postumus and successors) in Gaul and local rulers in Syria, restoring unity to the Imperial core. Probus (276-282) finally secured the Rhine and Danube frontiers, employing armies of barbarian rank-and-file. Carus (283-284) pushed an Eastern offensive to the Sassanid capital of Ctesiphon, but was killed, perhaps by lightning. His sons were elevated by prior arrangement to Augustus (emperor) and Caesar (junior emperor). The former was killed, whereupon the important general Diocletian had his troops acclaim him, and then defeated the remaining Caesar to take the throne.
While noting some changes within the constitution of the Roman state, a forecaster at the time of M. Aurelius' ascent to the throne would have been justified in predicting continued Imperial peace and prosperity. Marcus was extremely talented, as had been his recent predecessors. A smooth interaction had of late emerged between Emperor and Senate, with the latter still respected, even as the administration and executive powers became larger, more effective, and less needful of the Senators. Peace had been the dominant trend, though offensive wars had increased the treasury due to booty. Thus, taxes had been reduced somewhat. At the same time, laws had been regularized, and after uncertainty during the first-century CE, the method of imperial succession had been tacitly established through Emperors adopting qualified officials as sons. As far as changes in the system, close observers would have noticed a slight broadening of political enfranchisment at the top of society. Provincials with the necessary wealth or education were allowed into the Senate or Imperial service, as Emperors themselves now descended from Italian families that had settled outside of the peninsula. As well, a law proclaiming Latin Rights bestowed a status on not-Italians that edged ever-closer to full citizenship.
In this sense, then, the reign of Marcus Aurelius and its direct aftermath is the dividing point between the Roman zenith and decline. Key trends of fateful significance to later Roman rule emerged during his tenure. These include 1) large scale raiding by a shifting patchwork of Germanic Barbarian tribes as opposed to organized conflict with regular opposing armies; 2) tremendous fiscal challenges and burdensome government measures in order to financially support warfare; 3) military conflict on two frontiers separated by thousands of miles; 4) the emergence of the Palace Guard and field legions as king-makers; 5) destabilization in procedures of Imperial succession; and 5) the widening of the leadership class beyond those who grew up in a thoroughly Latinized milieu. It is thus ironic and sad that Marcus Aurelius was a superlative philosopher, Stoicist, and equitably-minded product of Roman culture, as he spent all of his career on horse-back fighting those who would overwhelm his state and culture three hundred years later.
Beyond Commodius' illustration that second-century emperors could be just as venal and ill-equipped as had been Caligula (r. 37-41) and Nero (r. 54-68), the period commencing with the Severan dynasty (193 CE) and ending with Constantine's death (337 CE) exhibits basic changes in the form of Roman state and society. These changes are essential to an understanding of the last decades of the Roman state in the West, the roots of Byzantium, and the first era of post-Roman Europe.
In political terms, the changes can be best summed up as culminating a process of change from Republic to Principate to Dominate. The ideal of Roman society had always been a republic ruled by a senate that expressed the will of citizens by electing consuls whose tenures were limited. This was an ideal, in that only residents of Italy were counted as citizens, and equality was more between senators and consuls than among the populace as a whole. From the time of Julius Caesar (d. 44 BCE), however, the power of the individual leader had begun to increase in proportion to that of the Roman Senate. Ultimately, Octavian Augustus (r. 27 BCE-13 CE) established a Principate. Theoretically, the Princeps, or Emperor was close to being an equal to the Senate, or primus inter pares (first among equals). He and his successors for at least a century respected the Senate, reserved to it important fiscal, municipal, and appointive functions, and co-opted some of its members into the imperial bureaucracy as well as military roles. In truth, though, the power of the Princeps was beyond challenge, especially with the ascent of war-proven leaders at crucial times, such as Vespasian, Titus, Trajan, and Hadrian (69-120 CE). Still, almost every single emperor was of Italian origin or at least high-born and heavily schooled in Latin culture, and saw himself in such a perspective. The philosopher-king Marcus Aurelius was one of the last of these (r. 161-180 CE).
Contemporaneous with Aurelius, however, Barbarian incursions began along the Rhine and Danube. This opened the way for the ascent of a new kind of general and then emperor, which the Severi embodied. Increasingly non-Latin soldier emperors who proved their mettle on the battlefield, these Emperors have been called variously military emperors, camp-made, or barracks-room emperors. While these men were usually committed to pragmatic problem solving and maintenance of imperial frontiers, rapid and volatile imperial succession wreaked havoc on the Roman body politic. Further, as Balkan peasants, with partially barbarian backgrounds, it cannot be sure that they or their Balkan-German soldiers fully comprehended the Roman ideal they were protecting.
Problems of imperial continuity also point to the major 'Achilles heel' of Roman politics: imperial succession. Beyond hereditary rule, which was disconcerting to the Roman civic tradition, the Romans had never worked out a good system. Even in particularly problematic times though, such as the Year of the Four Emperors (68-69 CE), overall coherence of the imperial system, and persistence of local, senatorial, provincial administration had worked through the difficulties. Now, with foreign military pressures and their economic ramifications, political destabilization mattered much more. From 235-85, more than 20 plausible emperors were acclaimed by their armies. For the first time in generations, Pax-Romana cracked on the Rhine, in Gaul, and along the Danube.
Along with these changes in leadership dynamics were also economic changes, particularly in the provincial, agricultural sector. From the end of the first century, senators and other rural elites started to acquire large landholdings, farmed by hired labor. Called latifundia, these landholdings constituted a change from previously dominant small peasant landholdings in Gaul especially. Not only did this new arrangement cut down on the numbers of owners able to pay taxes, but latifundians often evaded tax obligations. In both cases, Barbarian incursions may have lessened capacity to pay. These changes in socio-economic relations meant that peasants could no longer be the tough citizen-soldier reservoir of the past. Also, aristocrats were no longer the best option for military leadership, since, assuming they were willing to leave their holdings, they could threaten insecure military emperors. Similarly, the town bourgeoisie had grown accustomed to peace and were not ideal soldiers. The military source of preference for the new emperors was either the Balkan peasantry they knew by blood ties, or Germans, to whom some third- century leaders were also connected by birth. Thus began the Germanization of the army proper, seeping eventually into the high command.
This turn of events was problematic, as Barbarian migrations of varying degrees of destructiveness were a dynamic lasting to the end of the Empire. Indeed, by the mid-third century, there was little ethnic difference between Roman armies and the Barbarian forces they fought. Further, continuous conflict, both in the West and against resurgent Persians under the Sassanids, meant that geographically wide-ranging military commitments outstripped military manpower, and sections of impossibly long borders were denuded of soldiers.