Byzantine Solidus

The Byzantine solidus maintained an astonishing consistency in its gold content—about 4.5 grams of nearly pure metal—for over a millennium, outlasting most empires.

This made it a reliable backbone for trade across the Mediterranean, from the courts of Constantinople to distant markets in India. Struck initially under Constantine in the early 4th century, its design evolved subtly, featuring emperors' portraits that grew more stylized over time. We know variations existed, like the light weight solidus introduced later, but exact mintages for many periods are lost to history.

One oddity: after examining hundreds, I've noticed how these coins often turn up in hoards, as if they were the empire's way of hiding its wealth from the next invasion.