Alexios I debases the Byzantine hyperpyron
Emperor Alexios I Komnenos debased the Byzantine gold coin in 1092, after nearly 700 years of stability. He introduced a new coin, the hyperpyron, with about 20.5 carats gold content (roughly 85 percent purity) versus the old solidus at 24 carats. The debasement reflected the collapsing Byzantine fiscal position after the 1071 Battle of Manzikert and the loss of most of Anatolia. Alexios tried to reform the whole coinage system around the new standard, but the break was done: the most stable currency in the history of the ancient world had been debased, and the Byzantines would continue debasing it across the next 200 years.
The original solidus was introduced in 312 AD. By the time Alexios debased it in 1092, the coin had maintained roughly the same gold content through the fall of Rome, the rise of Islam, the Crusades, and three Byzantine dynasties. Its collapse marked the end of Mediterranean monetary unity.
02 · Royal Debasement
With the fall of Rome and the fragmentation of Europe into feudal kingdoms, each monarch controlled their own mint. The temptation to debase was structural: a king who recalled all the silver coins in circulation, melted them, and re-struck them with less silver per coin kept the difference as seigniorage. Across 500 years, nearly every European kingdom did this at least once. The most spectacular was Henry VIII's Great Debasement of 1544 to 1551, which cut the silver content of the English shilling from 92.5 percent to 25 percent in seven years.
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