Aulus Vitellius was Roman Emperor for eight months, from 19 April to 20 December AD 69. Vitellius was proclaimed emperor following the quick succession of the previous emperors Galba and Otho, in a year of civil war known as the Year of the Four Emperors. His claim to the throne was soon challenged by legions stationed in the eastern provinces, who proclaimed their commander Vespasian emperor instead. War ensued, leading to a crushing defeat for Vitellius at the Second Battle of Bedriacum in northern Italy. Once he realized his support was wavering, Vitellius prepared to abdicate in favor of Vespasian. He was not allowed to do so by his supporters, resulting in a brutal battle for Rome between Vitellius' forces and the armies of Vespasian. He was executed in Rome by Vespasian's soldiers on 20 December 69.

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Proclaimed emperor in 193 by his legionaries in Noricum during the political unrest that followed the death of Commodus, he secured sole rule over the empire in 197 after defeating his last rival, Clodius Albinus, at the Battle of Lugdunum. In securing his position as emperor, he founded the Severan dynasty.

Caracalla was assassinated while en route to a campaign against the Parthians by the Praetorian Guard.

On April 8, 217, Caracalla was assassinated traveling to Carrhae. Three days later, Macrinus was declared Augustus. Diadumenian was the son of Macrinus, born in 208. He was given the title Caesar in 217, when his father became augustus, and raised to co-Augustus the following year.