The Dominate
The accession to the purple on November 20, 284, of Diocletianus, the lower-class, Greek-speaking Dalmatian commander of Carus's and Numerianus's household cavalry (protectores domestici), marked a major departure from traditional Roman constitutional theory regarding the Emperor, who was nominally first among equals; Diocletianus introduced Oriental despotism into the Imperial dignity. Whereas before Emperors had worn only a purple toga (toga purpura) and greeted with deference, Diocletianus wore jewelled robes and shoes, and required those who greeted him to kneel and kiss the hem of his robe (adoratio). In many ways, Diocletianus was the first monarchical Emperor, and this is symbolised by the fact that the word dominus ("Lord") rapidly replaced princeps as the favoured word for referring to the Emperor.
- Diocletianus ("Imp. Caesar C. Aurelius Diocletianus P.F. Invictus Aug."; b. Dioclκs), 284 - 293
- Maximianus ("Imp. Caesar M. Aurelius Valerius Maximianus P.F. Invictus Aug."; b. Maximianus), 286 - 293
The Tetrarchy
The Tetrarchy was a system established by Diocletianus to facilitate effective government of the Empire. There were two senior emperors (augusti), one for the West and one for the East, and two junior sub-emperors (caesares), one for each senior emperor. When the senior emperors left office for whatever reason, the junior sub-emperors would become senior emperors and appoint their own junior sub-emperors; the retired senior emperors took the title senior augustus and were styled Patres Imperatorum et Caesarum ("Fathers of the Imperators and of the Caesars").
Emperors in the East
- Augustus: Diocletianus (cont'd.), 293 305
- Caesar: Galerius ("Galerius Valerius Maximianus Nob. Caesar"; b. Galerius Valerius Maximianus), 293 305
- Augustus: Galerius ("Imp. Caesar Galerius Valerius Maximianus P.F. Invictus Aug."; b. Galerius Valerius Maximianus), 305 311
- Caesar: Maximinus "Daia ("C. Valerius Galerius Maximinus Nob. Caesar"; b. C. Valerius Galerius Maximinus), 305 311
- Augustus: Maximinus "Daia ("Imp. Caesar Valerius Galerius Maximinus P.F. Invictus Aug."; b. C. Valerius Galerius Maximinus), 311 313
Emperors in the West
- Augustus: Maximianus (cont'd.), 293 305
- Note: Maximianus had been co-Emperor with Diocletianus from 286 to 293 prior to the establishment of the Tetrarchy
- Caesar: Constantius I "Chlorus ("C. Flavius Valerius Constantius Nob. Caesar"; b. C. Flavius Valerius Constantius), 293 305
- Augustus: Constantius I "Chlorus ("Imp. Caesar Flavius Valerius Constantius Aug."; b. C. Flavius Valerius Constantius), 305 306
- Caesar: Severus ("Flavius Valerius Severus Nob. Caesar"; b. Flavius Valerius Severus), 305 306
- Augustus: Severus ("Imp. Caesar Severus P.F. Aug."; b. Flavius Valerius Severus), 306 307
- Caesar: Constantinus I ("Flavius Valerius Constantinus Nob. Caesar"; b. C. Flavius Valerius Constantinus), 306 307
- Note: Constantius's soldiers had proclaimed Constantinus augustus immediately upon Constantius's death on July 25, 306, but the augustus in the East, Galerius, acknowledged him only as caesar to Severus
- Augusti: Maxentius ("Imp. Caesar M. Aurelius Valerius Maxentius P.F. Invictus Aug."; b. M. Aurelius Valerius Maxentius) and Maximianus ("Imp. Caesar M. Aurelius Valerius Maximianus P.F. Invictus Aug."; b. Maximianus), 307 308
- Caesar: Constantinus I (cont'd), 307 308 (styled "Imp. Caesar Constantinus P.F. Invictus Aug." from 307)
Note: In 307, the augustus Severus was murdered by mutinous soldiers while attempting to suppress the rebellion and usurpation of Maxentius, who had invited his father Maximianus to return from retirement and reassume the purple as augustus with him. Maxentius and Maximianus reigned in the West as augusti co-operating with Constantinus as caesar until the Imperial conference at Carnutum in November 308, whereat Constantinus confirmed as caesar, Maximianus deposed, and Licinius appointed augustus in his place. Maxentius continued to hold power as a rival Emperor until 312; his father Maximianus (the first Emperor to be restored) committed suicide after an attempt to don the purple a third time in 310.
- Augustus: Licinius ("Imp. Caesar C. Valerius Licinianus Licinius P.F. Invictus Aug."; b. C. Valerius Licinianus Licinius), 308 313
Tetrarchical Relationships
Diocletianus's wife Prisca bore him a daughter Galeria Valeria, who married Galerius (whom Diocletianus had adopted and appointed caesar on March 1, 293). Galerius's sister gave birth to a son, Maximinus Daia, and Galerius's daughter by his first wife, Valeria Maximilla, married Maxentius, son of Maximianus by his wife Eutropia; Eutropia's first marriage (to Afranius Hannibalianus) had produced a daughter, Theodora, who became the second wife of Constantius I "Chlorus" ("the Pale") in 289 (adopted by Maximianus on March 1, 293). Constantius's marriage to Theodora produced a daughter, Constantia, who married Licinius; his first marriage to St. Helena produced a son, Constantinus (see below), whose second wife was Fausta, sister of Maxentius and daughter of Maximianus.
To summarise:
- Diocletianus: father-in-law and adoptive father of Galerius
- Maximianus: father of Maxentius, adoptive father and stepfather-in-law of Constantius I "Chlorus", father-in-law of Constantinus, stepgrandfather-in-law of Licinius
- Galerius: son-in-law and adopted son of Diocletianus, uncle of Maximinus Daia, father-in-law of Maxentius
- Constantius I "Chlorus": father (and stepbrother-in-law) of Constantinus, father-in-law of Licinius, adopted son and stepson-in-law of Maximianus, adoptive brother and half-brother-in-law of Maxentius
- Maximinus Daia: nephew of Galerius
- Constantinus: son (and stepbrother-in-law) of Constantius I "Chlorus", son-in-law of Maximianus, brother-in-law of Maxentius, half-brother-in-law of Licinius
- Maxentius: son of Maximianus, son-in-law of Galerius, adoptive brother and half-brother-in-law of Constantius I "Chlorus", brother-in-law of Constantinus
- Licinius: son-in-law of Constantius I "Chlorus", half-brother-in-law of Constantinus, half-nephew of Maxentius, stepgrandson-in-law of Maximianus