Galerius (260-311) was of Illyrian descent. His parents were peasants and he himself, before rising to the senior hierarchy in the Roman army, had been a shepherd. Galerius, who was adopted and appointed Caesar (293-305 A.D.) by Diocletian on March 1, 293 A.D., assumed responsibility for protection of the empire’s eastern frontiers. His marriage to Galeria Valeria, the daughter of Diocletian, followed (or preceded, according to some) this event.
After Diocletian resigned on May 1, 305 A.D., Galerius was proclaimed Augustus at Nikomedeia (305- 311 A.D.).
The construction of the palace in Thessaloniki began in the late third century A.D. when Galerius concluded his victorious campaign against the Persians by defeating their king, Narseh, in Armenia (298 A.D.). After this important victory, which led to a peace on terms highly favorable to the Romans, the emperor returned to the Balkans (299 A.D.) and established Thessaloniki as his seat.
According to most scholars, the city was Galerius’ seat during two periods: from 299-303, and from 308 until his death in 311 A.D. This is confirmed by the operation of the mint in Thessaloniki (299-303, 305-308 A.D.), the ruins of the palace complex, and the iconographic program featured on the triumphal arch (Kamara), which illustrates his victory over the Persians. There are also references to Galerius’ staying in Thessaloniki in later hagiographic texts, where he is mentioned as a persecutor of Thessaloniki’s Christian martyrs.
During the period Thessaloniki was serving as Galerius’ imperial headquarters, it emerged as the most important center in the greater region, a city where the building and decorative arts found fertile ground for development.
Galerius died after a serious illness in 311 A.D., and was buried in his birthplace Romuliana, which was thus named in honor of his mother Romula. The ruins of Romuliana have been revealed near the modern town of Gamzigrad in eastern Serbia. Excavations carried out in the 1950s brought to light the building remains of a small walled palace to which the emperor would have withdrawn upon surrendering his power. The mausoleums of Galerius and his mother have been found on the neighboring hill of Magura.
The final political act of the emperor shortly before his death was the publication on April 30, 311 A.D. of the Edict of Toleration of Christianity, which heralded the definitive end to the persecution of Christians; toleration was fully established by Constantine the Great with the Edict of Milan (313 A.D.).