Roman usurper Emperor Allectus - $700k

Formerly the finance minister (rationalis) to the usurper Carausius, Allectus seized the throne by assassinating Carausius before being defeated and killed by the Roman Caesar Constantius Chlorus in 296 AD. Constantius was bestowed the title Britannicus Maximus. The Allectus aureus was estimated to sell for between $90k and $127k in 2019. Warring bidders pushed that to $700k.

A metal detectorist found a gold coin in Kent with the image of the Roman Emperor Allectus with two kneeling captives at the feet of the god Apollo on the obverse. In power from 293 to 296 AD, Allectus was one of two Roman emperors who ruled Britannia and northern Gaul as an independent nation between 286 and 296 AD. The British Museum owns the only other known example of this Allectus aureus, and nobody has found any coin bearing his visage in over 50 years.

Constantius Chlorus rose from obscurity to become the Emperor of the western Roman empire. A soldier who worked his way up through the ranks, his star rose in 289 after he married Theodora, the stepdaughter of the emperor Maximian. By this time Constantius had already fathered a soon to be famous son named Constantine by another woman, Helena. The Arras Medallion (AD 296) celebrating his victory weighs 26.79 gms.

A bronze antoninianus coin of Allectus is notable for the history it reflects. The coin realized a hammer price of €550 ($618 U.S.) against a pre-sale estimate of €200 ($225 U.S.). Slender and shallow ships were used in Roman rivers until late antiquity and played a significant military role. The ship was easy to navigate and thus sailors could be trained quickly. Each carried 50 men, with 30 of them rowing.