After the assassination of Aurelian, Tacitus was chosen by the Senate to succeed him as Roman emperor.

Aurelian was a Roman emperor who reigned from 270 to 275 AD during the Crisis of the Third Century. As emperor, he won an unprecedented series of military victories which reunited the Roman Empire after it had nearly disintegrated under the pressure of barbarian invasions and internal revolts. For his success in restoring the Empire's territorial integrity, Aurelian was honored with the title Restitutor Orbis. Born in modest circumstances, most likely in Moesia Superior, he entered the Roman army in 235 and climbed up the ranks. He went on to lead the cavalry of the emperor Gallienus, until Gallienus' assassination in 268. Following that, Claudius Gothicus became emperor until his own death in 270. Claudius' brother Quintillus then ruled for three months, before Aurelian took the empire for himself. Aurelian was chosen Roman emperor by the Illyriciani as one of themselves.

Marcus Claudius Tacitus was Roman emperor from 275 to 276. During his short reign he campaigned against the Goths and the Heruli, for which he received the title Gothicus Maximus.

The Roman Senate was the highest and constituting assembly of ancient Rome and its aristocracy. With different powers throughout its existence, it lasted from the first days of the city of Rome as the Senate of the Roman Kingdom, to the Senate of the Roman Republic and Senate of the Roman Empire and eventually the Byzantine Senate of the Eastern Roman Empire, existing well into the post-classical era and Middle Ages.

The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title augustus to Octavian in 27 BC. The term emperor is a modern convention, and did not exist as such during the Empire. When a given Roman is described as becoming emperor in English, it generally reflects his accession as augustus, and later as basileus. Another title used was imperator, originally a military honorific, and caesar, originally a cognomen. Early emperors also used the title princeps alongside other Republican titles, notably consul and pontifex maximus.