e. Aurelian regarded himself as an
absolute monarch and employed on his coins the titles _dominus et deus
natus_--"born Lord and God." He likewise reestablished in Rome the official
cult of the Unconquered Sun God, previously introduced by Elagabalus. One
of the characteristics of this cult was the belief that the monarch was
the incarnation of the divine spirit, a belief which gave a moral
justification to absolutism.

*Probus, 276-282 A. D.* Aurelian was murdered in 275 A. D., and was
succeeded by Tacitus, who met a like fate after a rule of less than two
years. He was followed by Marcus Aurelius Probus, an able Illyrian
officer. Probus was called upon to repel fresh invasions of Germanic
peoples, to subdue the rebellious Isaurians in Asia Minor and suppress a
revolt in Egypt. Everywhere he successfully upheld the authority of the
empire, but his strict discipline eventually cost him the favor of the
soldiers who hailed as Imperator Marcus Aurelius Carus. Probus was put to
death (282 A. D.). Like his predecessor, Carus was a general of great
ability. He appointed his eldest son Carinus Augustus as his co-ruler, and
left him in charge of the West while he embarked on a campaign against the
Persians. This was crowned with complete success and terminated with the
capture of Ctesiphon. But on his return march he died, probably at the
hands of his troops (283 A. D.). His younger son, the Caesar Numerianus,
who took command of the army, was assassinated by the praetorian prefect
Aper. However, the choice of the army fell upon Gaius Valerius Aurelius
Diocletianus, who assumed the imperial title in September, 284 A. D. But
Carinus had retained his hold upon the West and advanced to crush
Diocletian. In the course of a battle at the river Margus in Moesia he was
murdered by his own officers (285 A. D.), and with the victory of
Diocletian a new period of Roman history begins.

CHAPTER XIX

THE PUBLIC ADMINISTRATION UNDER THE PRINCIPATE

I. THE VICTORY OF AUTOCRACY

*The senate and the appointment of the princeps.* In the preceding
chapters we have traced in outline the political history of the principate
to the point where it had become an undisguised military autocracy. This
change is clearly seen in connection with the imperial nomination. The
appointment to the principate originally involved the conferment of the
_imperium_, the tribunician