The Acession to Power of Vespasian (the beforemath)
The World Starts to Crumble Beneath Nero's feet
The political collapse of 68-69 AD in Rome began after several years of peace and prosperity, maintained under Nero during the first five years of his reign, "The Golden Years" of Nero. Many of the problems which arose could be attributed to personal issues that the emperor had, and his general characteristics, strategy, or lack of strategy. One of the biggest factors was Nero's disinterest in military conquest, or anything having to do with the military, as he basically ignored it. The lack of a central authority or figurehead in the Roman army became a problem because Nero no longer followed the advice of his advisors, including that of Seneca. Thus the army became fragmented and, like the era of Marius and Sulla and the personal army, armies became loyal to their local generals.
Nero bankrupted or nearly bankrupted the empire's treasury through extravagant building projects, one of which was his personal palace after the fire in Rome. Nero began to devalue the Roman coinage to fund his expenditures and then started to accuse wealthy aristocrats on varying and false charges in order to seize their property and wealth. Gradually, Nero alienated those whose support was necessary for him to stay in power -- the conservative upper class grew a distaste for Nero's un-Roman policies and activities and unjust seizure of estate as well as decreased senatorial power. Because he had not been involved at all with the military, Nero also lacked the support of legions outside Rome and the Praetorian Guard, and putting his loyal and successful general, Domitius Corbulo, to death in 67 on suspicion of conspiracies certainly did not help matters.
Three emperors come and gone
All of these factors were involved when Vindex, governor of a province in Gaul, led a revolt in April of 68 AD. Rufus, general of the Roman army in Germany, crushed the revolt with three legions and his army proclaimed him as emperor. Rufus refused the seat and the honor, but the precedent had been set as people realized that wherever there was an army, there could be an emperor. The discovery of this arcana imperii, or secret of power, led to armies in other regions creating their own emperors.
Galba, general of the armies in Spain, was proclaimed emperor by his armies and then was recognized by the senate in October of 68 as princeps. However, he was an ineffective leader, refusing to pay a promised bonus to the Praetorian Guard and ending the grain distrubituion. His inflexibility alienated many, and he was assassinated January 15th of 69, after an army elsewhere (Germany) had procaimed Vitellius emperor on January 3rd.
Meanwhile in Rome, the Praetorian Guard declares that Otho is emperor, and are loyal to him. In April of 69, Otho and Vitellius' armies meet in Northern Italy, and Otho commits suicide in order to save Rome from the destruction and violence of another civil war. The senate then recognizes Vitellius as emperor. Vitellius, however, was also ineffective at ruling and was unable to stop the violence and looting after his victory.
Vespasian, however, enters the scene. His brother, Sabinus, is prefect in Rome. The death of Sabinus and other confusion leads to Vitellius being killed. Vespasian might have suffered the same fate of these other emperors who were in power for less than a year, had it not been for two important factors which were out of his control -- luck and an heir, and his character, as he possessed common sense and tended to act with great caution in all things. One of Vespasian's potential rivals, the general Mucianus had also decided to throw his support behind Vespasian, and put down many other potential rivals and revolts. The fact that Vespasian already had a set heir could have also dissuaded some ambitious leaders from revolting because of consequences down the road. The lack of central authority in the Roman army which led to the end of Nero's reign was also solved under Vespasian, who inherited low level soldiers from Mucianus and Corbulo, and defeated rivals and had support of legions in several different provinces.
source: lectures of Ronald Mellor, a wonderful professor of Roman History at UCLA. this writeup was based on an in-class midterm essay.