Double sestertius

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The double sestertius was a large Roman coin made of orichalcum (a gold-brass alloy) issued around AD 249–251 by Emperor Trajan Decius to fight inflation that lowered the value of the ordinary sestertius. In reality, it wasn’t much bigger than the regular sestertius, which had already become lighter and smaller. It’s usually called a "double" sestertius, but it was probably worth only about 1.5 sestertii.

It faded from use, but the rebel emperor Postumus (AD 259–268) revived it for a time, issuing his own version by overstriking worn old sestertii to add his portrait and legends, likely because of metal shortages. The Postumus issue ended in early 262.

After that, Roman coinage continued to decline, with the few circulating coins being very debased double-denarii, known as antoniniani or radiates (from the radiate crown). Older coins like the sestertius disappeared as they were melted down to make radiates. By the 4th century, even those had vanished and a new coin system had been created.