Constantius Chlorus, or Constantius I, was one of two original junior emperors, called Caesars, of the tetrarchy (“rule of four”). Diocletian instituted this new form of reign in response to the dynastic disasters that shaped the Third Century Crisis. The tetrarchy operated with two Augusti, Diocletian and Maximian, who each had one subordinate Caesar, Constantius and Galerius, to assist them in administering and protecting their portion of the empire. After twenty years, the two senior emperors would abdicate, and each Caesar would succeed them, appointing their own junior co-rulers in turn. The tetrarchy prospered in many ways – with more men to cover the expanse of the empire, it was able to address the growing fragility of the borders and frontiers, which were under threat on all sides from barbarian tribes. All the tetrarchs were also Illyrian soldiers (reflected by Constantius’ portrait on the obverse, with close-cropped hair and beard), making them ideal candidates for these aggressive military attentions. The reverse of this coin depicts their strength in unity, with the four emperors sacrificing together before a gate. The legend, “Victory over the Sarmatians” further emphasizes their martial success. However, the tetrarchy would dissolve after Constantius’ ascent to Augustus and death, when his son, Constantine, would be declared emperor and challenge the succession arrangement designed by Diocletian. KHK.