Coins from Tetrarchy
'Tetrarchy' means the government of four people, and was a system introduced in 293 AD by Roman Emperor Diocletian.

Under the Tetrachy, the sovereignty of the Roman Empire was divided amongst four people; two Augusti or 'Senior Emperors' and two Caesars or 'Junior Emperors'. The four emperors based themselves not in Rome, but in cities closer to the frontier, from which they could each oversee and protect a part of the Empire.

Unfortunately, the system was too naive - when Diocletians & Maximian's reigns were up they abdicated, but the next set of Augusti were less concerned with upholding the system and soon the Tetrarchs were at each other's throats.

By 313 AD, most of the Tetrarchs and claimants were dead, and by 324 the empire was once again united under Constantine the Great.

Tetrarchy

(1) Constantius I 293 AD
Obverse: laureate, draped and cuirassed bust right; ΦΛA KWCTANTIOC K
Reverse: Elpis standing left, holding flower and raising skirt; L_A / A
Ref: Geissen 3347; Milne 5089; Dattari 6...
(2) Diocletian 284-285 AD
Obverse: laureate, draped bust right; A K Γ OYAΛ ΔIOKΛHTIANOC CEB
Reverse: Elpis standing left, holding flower and raising skirt; LA
Ref: Milne 4750; Curtis 1980; Geissen 32...
(3) Diocletian 285-286 AD
Obverse: laureate and cuirassed bust right; A K Γ OYAΛ ΔIOKΛHTIANOC CEB
Reverse: Dikaiosyne (Aequitas) standing half left, holding scales and cornucopia; L_B
Ref: Milne 4770; Curtis 1967; Dattari 56...
(4) Diocletian 290-291 AD
Obverse: laureate head right ΔIOKΛHTI_ANOC CEB
Reverse: Zeus standing half left, wearing chalmys, holding patera and scepter. eagle at feet; L_Z
Ref: Milne 4946; Curtis 2045; BMC Alexan...
(5) Maximian 291-292 AD
Obverse: laureate, draped and cuirased bust right; MAΞIMI_ANOC CEB
Reverse: Nike with wreath and palm branch advancing right; L_* / Z
Ref: Milne 5031, Curtis 2101, Geissen 33...