Solidus (coin)

The solidus was a high-purity gold coin issued in the late Roman Empire and subsequently by the Byzantine Empire. Introduced by Emperor Constantine the Great around 312 AD, it replaced the aureus as the standard gold coin. The solidus was significantly lighter than the aureus, weighing approximately 4.5 grams of pure gold.

The introduction of the solidus was a key part of Constantine's monetary reforms, aimed at stabilizing the Roman economy. Its consistent weight and purity helped to restore confidence in Roman currency and facilitate trade both within the empire and with foreign powers.

The solidus remained the standard gold coin of the Byzantine Empire for centuries, with its design and purity largely unchanged until the 11th century. During this period, it was a highly respected and widely accepted currency throughout the Mediterranean world and beyond. It served as a model for other gold coins, such as the dinar issued by various Islamic caliphates. Over time, debasement of the solidus began to occur, diminishing its value and contributing to economic instability in the later Byzantine era. The name "solidus" is the origin of several currency names, including the French "sou" and the Italian "soldo."