Diocletian (c. 245-c. 312) came from Dalmatia (modern Croatia). Of low birth, he rose to prominence through a successful military career. As emperor, he increased the number of troops and installed them along the empire's borders. War with Persia during his reign led to Roman territorial gain along that border.
Diocletian ended the "Crisis of the Third Century" (235-284) by giving up sole control of the Empire, thereby ending the Principate and starting the Dominate (rare), from the word dominus 'lord' now used to describe the emperor. Diocletian set up the rule by 4 known as the Tetrarchy. Instead of dying in office, as all earlier emperors had done, Diocletian abdicated and retired to his palace at Split where he gardened.
Although he split the empire and gave up his post, Diocletian was not a modest emperor. Kneeling before the emperor to kiss his hem started with Diocletian. He adopted other signs of royalty from Persia, as well. Edward Gibbon paints a lavish picture of his accessories:
"Their principal distinction was the Imperial or military robe of purple; whilst the senatorial garment was marked by a broad, and the equestrian by a narrow, band or stripe of the same honorable color. The pride, or rather the policy, of Diocletian, engaged that artful prince to introduce the stately magnificence of the court of Persia. He ventured to assume the diadem, an ornament detested by the Romans as the odious ensign of royalty, and the use of which had been considered as the most desperate act of the madness of Caligula. It was no more than a broad white fillet set with pearls, which encircled the emperor's head. The sumptuous robes of Diocletian and his successors were of silk and gold; and it is remarked with indignation, that even their shoes were studded with the most precious gems. The access to their sacred person was every day rendered more difficult by the institution of new forms and ceremonies."
- "Diocletian" Oxford Dictionary of the Classical World. Ed. John Roberts. Oxford University Press, 2007.
- "The Legions of Diocletian and Constantine"
H. M. D. Parker
The Journal of Roman Studies, Vol. 23, (1933), pp. 175-189
- "Diocletian's Palace at Split"
A. J. Brothers
Greece & Rome, Second Series, Vol. 19, No. 2 (Oct., 1972), pp. 175-186.