Europe 305: Second Tetrarchy
In 305 Diocletian and Maximian both retired, setting a precedent in the hopes of stabilizing the office of Emperor and preventing further succession crises. Galerius and Constantius became the new Augusti and appointed Maximinus Daza and Valerius Severus as their Caesars.
The Agri Decumates was lost to the Romans in c.262, regained by Aurelian and Probus in 275–8, and lost again sometime between 290 and 310. The losses here seem not so much due to any rise in power of the local Alemanni tribe, but Roman internal division. When rival Roman factions controlled Gaul and Raetia, as was the case in 262–274 and 306, the limes of the Agri Decumates were no longer defensible and had to be abandoned.
302? Battle of Vindonissa▲
Following the Battle of Lingones, Constantius intercepted and destroyed a large body of Alemanni near Vindonissa (Windisch, Switzerland). A third encounter occurred in winter or early spring, when a great many Germans from many different tribes attempted to cross the frozen Rhine but were trapped on an island by the unexpected thawing of the river. Embarking on boats, Constantius’ troops soon compelled the would-be invaders to surrender.
23 Feb 303–30 Apr 311 Great Persecution▲
In February 303 Diocletian began a campaign of persecution against the growing Christian population of the Roman Empire, ordering the destruction of churches and scriptures, the arrest and imprisonment of church leaders, and the deprivation of Christians of their legal rights and ranks. Hundreds, possibly thousands, were also executed for refusing to comply with demands to sacrifice to the Roman gods. After the abdication of Diocletian, the persecution continued in the East under Galerius until 311, but was abandoned in the West by 306.
303? Arsacid Albania▲
Following the Treaty of Nisibis (299), the Arsacid dynasty overthrew the Sasanian Persian proxies in the Caucasian Kingdom of Albania and its first king, Vachagan the Brave, became a client of Rome. The details of this event are uncertain, but a Sasanian rock relief in Fars shows Shah Hormizd II (r. 303–309) toppling a viceroy of Albania in an otherwise unrecorded conflict.
305 Afrighid Kingdom▲
In 305 the Khwarazmian leader Afrig expelled the Sasanians from Khwarazm and established the Afrighid dynasty. Although often forced to recognize the suzerainty of stronger neighbors, the Afrighids would rule over Khwarazm from their capital at Kat for a span of 690 years.
1 May 305 Second Tetrarchy▲
On 1 May 305, in simultaneous ceremonies in Nicomedia and Mediolanum, Diocletian and Maximian both retired, setting a precedent in the hopes of stabilizing the office of Emperor and preventing further succession crises. Constantius Chlorus and Galerius became the new Augusti, but remained based in Gaul and the Balkans, respectively. Although Constantius was technically the senior Augustus, Galerius was Diocletian’s informal successor and appointed his own officers, Valerius Severus and Maximinus Daza, as Caesars.
1 May 305–? May 311 Reign of Galerius▲
In 305 Galerius, then in his late 40s, succeeded Diocletian as Augustus in the eastern Roman Empire. Although Constantius Chlorus in the west was technically the senior Augustus, Galerius appointed both Caesars and informally dominated the empire east of Gaul and Spain even before Constantius’ death the following year. Nonetheless, Galerius struggled and ultimately failed to maintain the system of Tetrarchy that Diocletian had established and by his death in 311 the empire had split into five rival factions.