Solidus
The solidus was an important gold coin of late antiquity, introduced under Emperor Constantine the Great around 309/310 AD and remained a stable currency in the Eastern Roman and Byzantine Empires for centuries. In a numismatic context, the solidus marks the transition from Roman to Byzantine coinage and stands for continuity, stability and economic order in an era of profound upheaval.
The solidus replaced the previously used aureus, which had lost its value and significance as the gold coin of the Roman Empire due to weight fluctuations and inflation. Constantine’s reform established the solidus as a high-quality gold coin with a constant weight of approximately 4.5 grams (1/72 of a Roman pound). Its exceptional purity – usually over 95% fine gold – made it one of the most stable currencies of antiquity and the Middle Ages.
The introduction of the solidus was part of comprehensive economic and administrative reforms with which Constantine consolidated the Roman Empire. In everyday life in the Roman and Byzantine empires, the solidus was used primarily as a currency for invoicing and trade, rather than for everyday payments, as its high value meant it was reserved for high-value trade, tax payments and the remuneration of civil servants and soldiers.
The obverse of the solidus coins usually showed the portrait of the ruling emperor with imperial insignia such as a crown, armour or laurel wreath. The reverse bore symbolic motifs such as goddesses of victory, crosses, angels or depictions of Christ – especially in the Christian-influenced late antiquity and Byzantine era. These coin images served not only to legitimise rule, but also to spread ideological messages and portray the emperor as a ruler chosen by God.
The solidus was minted for more than seven centuries, particularly intensively in the Byzantine Empire. Under the name ‘nomisma’, it remained the backbone of the Byzantine coinage system until the 10th century. Even after its gradual disappearance from the 11th century onwards, the term ‘solidus’ lived on as a unit of account in Europe – for example, in the French abbreviation ‘s.’ for sol or in the British pound-shilling-penny notation ‘L.s.d.’ (libra, solidus, denarius).
In the context of numismatic collecting, the solidus is of great interest today. Its consistent quality, artistic portraits, historical significance and distribution across Europe, the Middle East and Africa make it a sought-after collector’s item. In addition, the solidus is an important source for research into the economy, trade, religion and representation of power in late antiquity and the early Middle Ages.