Galerius Maximianus (ca. 260–late April or early May 311), formally Gaius Galerius Valerius Maximianus was Roman Emperor from 305 to 311.
Galerius was born near Serdica, Thrace (now Sofia, Bulgaria), in the place where he later built his palace, Felix Romuliana (today Gamzigrad, Serbia). His father was a Thracian and his mother Romula was a Dacian woman, who left Dacia because of the Carpians attacks. He originally followed his father's occupation, that of a herdsman, where he got his surname of Armentarius (Latin: armentum, herd). He served with distinction as a soldier under Emperors Aurelian and Probus, and in 293 at the establishment of the Tetrarchy, was designated Caesar along with Constantius Chlorus, receiving in marriage Diocletian's daughter Valeria (later known as Galeria Valeria), and at the same time being entrusted with the care of the Illyrian provinces. Soon after his appointment, Galerius would be dispatched to Egypt to fight the rebellious cities Busiris and Coptos.
In 295 or 296, Narseh declared war on Rome. He appears to have first invaded western Armenia, retaking the lands delivered to Tiridates in the peace of 287. He would occupy the lands there until the following year. Narseh then moved south into Roman Mesopotamia, where he inflicted a severe defeat on Galerius, then commander of the Eastern forces, in the region between Carrhae (Harran, Turkey) and Callinicum (Ar-Raqqah, Syria). Diocletian may or may not have been present at the battle, but would present himself soon afterwards at Antioch, where the official version of events was made clear: Galerius was to take all the blame for the affair. In Antioch, Diocletian forced Galerius to walk a mile in advance of his imperial cart while still clad in the purple robes of an emperor. The message conveyed was clear: the loss at Carrhae was not due to the failings of the empire's soldiers, but due to the failings of their commander, and Galerius' failures would not be accepted. (It is also possible that Galerius' position at the head of the caravan was merely the conventional organization of an imperial progression, designed to show a Caesar's deference to his Augustus.)
Galerius had been reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings. Narseh did not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via Armenia. Diocletian may or may not have been present to assist the campaign. Narseh retreated to Armenia to fight Galerius' force, to Narseh's disadvantage: the rugged Armenian terrain was favorable to Roman infantry, but unfavorable to Sassanid cavalry. Local aid gave Galerius the advantage of surprise over the Persian forces, and, in two successive battles, Galerius secured victories over Narseh.
During the second encounter, Roman forces seized Narseh's camp, his treasury, his harem, and his wife along with it. Narseh's wife would live out the remainder of the war in Daphne, a suburb of Antioch, serving to the Persians as a constant reminder of Roman victory. Galerius advanced into Media and Adiabene, winning continuous victories, most prominently near Erzurum, and securing Nisibis (Nusaybin, Turkey) before October 1 298. He moved down the Tigris, taking Ctesiphon, and gazing onwards to the ruins of Babylon before returning to Roman territory via the Euphrates.
The conditions of the peace were heavy: Persia would give up territory to Rome, making the Tigris the boundary between the two empires. Further terms specified that Armenia was returned to Roman domination, with the fort of Ziatha as its border; Caucasian Iberia would pay allegiance to Rome under a Roman appointee; Nisibis, now under Roman rule, would become the sole conduit for trade between Persia and Rome; and Rome would exercise control over the five satrapies between the Tigris and Armenia: Ingilene, Sophanene (Sophene), Arzanene (Aghdznik), Corduene, and Zabdicene (near modern Hakkâri, Turkey). These regions included the passage of the Tigris through the Anti-Taurus range; the Bitlis pass, the quickest southerly route into Persian Armenia; and access to the Tur Abdin plateau. With these territories, Rome would have an advance station north of Ctesiphon, and would be able to slow any future advance of Persian forces through the region. Under the terms of the peace Tiridates would regain both his throne and the entirety of his ancestral claim, and Rome would secure a wide zone of cultural influence in the region. The fact that the empire was able to sustain such constant warfare on so many fronts has been taken as a sign of the essential efficacy of the Diocletianic system and the goodwill of the army towards the tetrarchic enterprise.
Christians had lived in peace during most of the rule of Diocletian. The persecutions that began with an edict of February 24 303, were credited by Christians to Galerius' work, as he was a fierce advocate of the old ways and old gods. Christian houses of assembly were destroyed, for fear of sedition in secret gatherings.
Diocletian was not anti-Christian during the first part of his reign, and historians have claimed that Galerius decided to prod him into persecuting them by secretly burning the Imperial Palace and blaming it on Christian saboteurs. Regardless of who was at fault for the fire, Diocletian's rage was aroused and he began one of the last and greatest Christian persecutions in the history of the Roman Empire.
It was at the insistence of Galerius that the last edicts of persecution against the Christians were published, beginning on February 24, 303, and this policy of repression was maintained by him until the appearance of the general edict of toleration, issued from Nicomedia in April 311, apparently during his last bout of illness, in his own name and in those of Licinius and Constantine (see Edict of Toleration by Galerius). Lactantius gives the text of the edict in his moralized chronicle of the bad ends to which all the persecutors came, De Mortibus Persecutorum ("On the Deaths of the Persecutors", chapters 34, 35). This marked the end of official persecution of Christians.
Galerius is remembered in Serbian mithology as herdsman emperor (car govedar)