1 March or 21 May 293[۱][۲]:۴, ۳۸[۳]:۲۸۸[۴]:۱۴۶[۵]:۶۴–۵[۶] – 1 May 305 (as Caesar, under دیوکلسین) 1 May 305 – late April or early May 311 (as Augustus alongside Constantius (until July 25, 306) then فلاویوس والریوس سوروس (until spring 307) then بیرینجی کونستانتین (from ca. September 307; unrecognized by Galerius' coinage from ca. September 307 to November 308) then لیسینیوس (from 11 November 308))[۲]:۴–۶
^The earlier dates for Galerius' appointment have been argued for based on the suggestion that the appointments of Constantius and Galerius were timed to coincide (Barnes 1981, 8–9; Southern 1999, 146). Barnes (1982, 62) argues against a dating of 21 May 293 in Nicomedia originating in Seston, Dioclétien, 88ff., stating that the evidence adduced (the Paschal Chronicle 521 = Chronica Minora 1.229 and Lactantius, DMP 19.2) is invalid and confused. Lactantius is commenting on Diocletian and the place where Diocletian was acclaimed, and that the "Maximianus" in the text is therefore a later gloss; the Paschal Chronicle is not authoritative for this period for events outside Egypt, and may simply be commenting on the day when the laureled image of the new emperors arrived in Alexandria. Potter (2004, 650) agrees that locating the acclamation to Nicomedia is false, but believes that Seston's other evidence makes a strong case for a temporal lag between the two Caesars' acclamations.
^Who’s who in the Roman world: "Galerius (C.250-311)"