On June 1, 193, Roman Emperor Didius Julianus was assassinated. From the article:
"The Year of the Five Emperors refers to the year 193 AD, in which there were five claimants for the title of Roman Emperor. The five were Pertinax, Didius Julianus, Pescennius Niger, Clodius Albinus and Septimius Severus. This year started a period of civil war where multiple rulers vied for the chance to become Caesar.The political unrest began with the murder of Commodus on New Year’s Eve 192 AD. Once Commodus was assassinated, Pertinax was named emperor but immediately had aroused opposition from the Praetorian Guard. They plotted and carried out his assassination. Pertinax was killed while resisting.[1] He was only emperor for three months. Didius Julianus succeeded Pertinax as emperor but was ousted by Septimius Severus and executed on June 1. Severus was declared Caesar by the Senate but Pescennius Niger was hostile when he declared himself emperor.[2] This started the civil war between Niger and Severus as both gathered troops and fought throughout the territory of the empire. Due to this war, Severus allowed Clodius Albinus, who he suspected as a threat to him, to be co-Caesar so that Severus did not have to preoccupy himself with imperial governance. This move allowed him to concentrate on waging the war against Niger.[1] Most historians count Severus and Albinus as two emperors even though they ruled simultaneously. The Severan dynasty was created out of the chaos of 193 AD.[2]"