The Solidus denomination
The solidus was a gold coin introduced by Diocletian in ad 301 as a replacement of the aureus. It was composed of relatively solid gold and minted 60 to the Roman pound. His minting was on a small scale, however, and the coin only entered widespread circulation under Constantine I after ad 312, when it permanently replaced the aureus.

The solidus was maintained essentially unaltered in weight, dimensions and purity until the 10th century.

The word soldier is ultimately derived from solidus, referring to the solidi with which soldiers were paid.
Solidus
(1) Leo I
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An AU Solidus struck 462-466 AD in Constantinopolis
Obverse: diademed, helmeted and cuirassed 3/4 facing bust, spear over shoulder; D N LEO PE_RPET AVG

Reverse: Victory standing left with long cross; VICTORI_A AVGGG B / * / CON OB

Diameter: 20 mm
Die Orientation: -
Weight: 4.42 g
No notes for this coin
RIC X 605, DOC 528
Roman Imperial (Eastern Empire)
(2) Valens
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An AU Solidus struck 369 AD in Nicomedia
Obverse: DN VALENS P F AVG, Bust of Valens facing right, wearing pearl diadem, cuirass, and drapery

Reverse: GLORIA REIPVBLICAE, Roma and Constantinople facing each other, each holding a scepter and together holding a shield inscribed VOT V MVLT X; SMNI in exergue

Diameter: 22 mm
Die Orientation: 5 H
Weight: 4.06 g
var is officina, 13b.2 is theta
RIC IX 13b.2 var.
Roman Imperial (Late Roman Empire)
(3) Valentinian II
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An AU Solidus struck AD 389-391 in Treveri
Obverse: D N VALENTINIANVS P F AVG, pearl-diademed, draped and cuirassed bust right

Reverse: VICTORIA AVGG, Valentinian II and Theodosius seated facing on throne, holding globe between them; palm between legs, figure of Victory with wings spread above; T-R across fields, COM in exergue

Diameter: 21 mm
Die Orientation: 1 H
Weight: 4.45 g
The first gold coin in my collection, and also the first coin I purchased by attending an auction in person!
RIC 90a; Depeyrot 53/1
Roman Imperial (Late Roman Empire)
(4) Valentinian III
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An AU Solidus struck 426-430 AD in Ravenna
Obverse: rosette-didemed, draped and cuirassed bust right; D N PLA VALENTI_NIANVS P F AVG

Reverse: Valentinian III facing, holding long cross and Victory on globe left, stepping on the human-headed serpent with closed-coiled; VICTORI_A AVGGG / R_V / CON OB

Diameter: 20.5 mm
Die Orientation: -
Weight: 4.4 g
No notes for this coin
RIC X Valentinian III 2011
Roman Imperial (Western Empire)
(5) Zeno
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An AU Solidus struck 476-491 AD in Thessalonica
Obverse: DN ZENO PERP AVG, Bust of Zeno facing slightly right, wearing helmet, pearl diadem, and cuirass, holding spear in right hand behind head and shield decorated with horseman on left arm

Reverse: VICTORIA AVGGG, Victory standing facing left, holding long jeweled cross; star in left and right fields; CONOB in exergue

Diameter: 20 mm
Die Orientation: 6 H
Weight: 4.28 g
Ex. Eliasberg
RIC X Zeno (East) 939
Roman Imperial (Eastern Empire)
(6) Zeno
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An AU Solidus struck 476 - 491 AD in Constantinople
Obverse: D N ZENO - PERP AVG: Bust of Zeno, helmeted, pearl-diademed, cuirassed, facing front, holding spear in right hand behind head and shield decorated with horseman on left arm

Reverse: VICTORI-A AVGGGΔ: Victory, winged, draped, standing right, supporting long jeweled cross; star in right field. MintMark: -/-//CONOB

Diameter: 20.5 mm
Die Orientation: 6 H
Weight: 4.46 g
Epsilon graffito in obv. field.
RIC X Zeno (East) 910
Roman Imperial (Eastern Empire)