Coins from Reform (491-602)
While the transition from Roman to Byzantine is gradual and somewhat fluid when it comes to political criteria, it is pretty clearly defined numismatically; In 491 Anastasius I became Emperor, and in 498 AD he introduced a monetary reform.

The new system involved three denominations of gold (the solidus and its half and third) and five of copper – the follis, worth 40 nummi, and its fractions worth 20, 10, 5 and 1 nummus. The obverses featured a highly stylized portrait, while the reverse featured the value in Greek numerals; M=40, K=20, I=10, E=5.

Politically this period covers Anastasius and the Justinian Dynasty, and was characterized by efforts to reclaim lost territory – North Africa, Illyria, southern Spain, and Italy. The last Justinian emperor – Maurice – managed to make himself unpopular enough to trigger a revolt which cost him his life in 602 AD, and triggered a series of cataclysmic events which would undo the progress of the last century.

Reform (491-602)

(1) Anastasius I 491-518 AD
Ref: None provided
(2) Anastasius I 491-498 AD
Obverse: draped, diademed bust right; (illegible letters)
Reverse: Monogram of Anastasius
Ref: BMC 32:128, Wroth 26
(3) Anonymous 530-580
Obverse: Helmeted, draped, cuirassed bust right,
Reverse: K
Ref: Vagi 3051; Bendall Type 8c
(4) Justin II Jan. 566 AD
Obverse: D N I - VST - INVS PP AVI, Helmeted bust facing, holding Victory on globe and shield.
Reverse: VICTORI - A AVGGG ? (officina 4) around, CONOB in exergue, Constantinipolis seated facing, head r., holding spear and cross on globe.
Ref: Berk-59, Hahn-4, Sear-344.
(5) Justinian I 539-540 AD
Obverse: DN IVSTINIANVS PP AVG, Bust of Justinian wearing helmet and cuirass, facing holding cross on globe and shield; cross to right
Reverse: Large M, ANNO to left, cross above, regnal year (XIII) to right, officina letter (ϵ) below; CON in exergue
Ref: SB 163
(6) Justin | Justinian | Justin II 518-578 AD
AE 12 nummi Alexandria
Obverse: Uncertain inscription, Bust facing right wearing diadem, cuirass, and drapery
Reverse: Cross between I and B; AΛEΞ in exergue
Ref: SB 112?
(7) Maurice Tiberius 590-602 AD
Obverse: DN mAVRC TIb PP AVG, Bust of Maurice facing, wearing plumed helmet, and cuirass, holding cross on globe
Reverse: VICTORIA AVGGI, Angel standing facing, holding long P-headed cross, and cross on globe; CONOB in exergue
Ref: SB 478
(8) Maurice Tiberius 593 AD
Obverse: D N MAVR TIBER PP AV. Helmeted and cuirassed bust facing, holding globus cruciger and shield.
Reverse: Large mark of value K; ANNO to left, cross above, X/I to right, A in exergue.
Ref: SBV 497; DOC 56a