The gold coin introduced by Constantine I that became a long-lasting Byzantine standard was the solidus.
Constantine introduced the solidus during his monetary reforms in the early fourth century, generally dated to around 309–312. It was a high-quality gold coin struck at 72 coins to a Roman pound, giving it a weight of roughly 4.5 grams. Its reliable weight and high gold purity helped restore confidence in imperial currency after decades of monetary instability and inflation.
The solidus replaced the aureus as the principal Roman gold coin and continued as the foundation of Byzantine gold coinage. In Greek, the Byzantine solidus was commonly called the nomisma. For centuries, governments used it to pay soldiers, officials, and large state obligations, while taxes and international trade also relied on its stable value.
The coin’s reputation lasted far beyond Constantine’s reign. Byzantine issues remained remarkably consistent in weight and purity until the eleventh century, although later reforms introduced lighter or altered denominations. The follis was primarily a copper coin, the hyperpyron was a much later Byzantine gold replacement, and the denarius was an older silver denomination.