It was minted in an exceptional year for the Roman Empire, when three emperors ruled jointly and Christianity became the official religion.
And now the extremely rare coin - which features a phoenix standing on a globe on one side - is to be auctioned off along with 72 other Roman coins.
The story of their discovery started in January 2020, when a metal detectorist searching a field in Colkirk near Fakenham found the first silver coin.
He recognised it as a siliqua from the late Roman period.
He spent the rest of the day searching and found 40 coins in total, and another 40 the next day.
Because of the Covid-19 lockdowns, it took two years before the excavations were complete, and 432 coins were eventually uncovered.
Nigel Mills, coin and artefact specialist at Noonans, which is auctioning the first tranche of 73 coins in Mayfair on Tuesday, December 5, said: “The hoard had, in fact, spread out over a third of an acre through disturbance by ploughing and has been recorded under the treasure act and returned to the finder after being disclaimed.
“The hoard is likely to have been deposited at the beginning of the 5th Century AD with the latest coin of Honorius dating no later than 402AD.
“Other Roman treasure finds of gold and silver also from East Anglia such as the Hoxne and Thetford hoards reflect the wealth and importance of the area.”
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Mr Mills said the tranche was expected to fetch £10,000-£12,500, but the coin with the phoenix was only the fifth specimen of its kind known to exist, and the other four were in museums.
He said it alone could sell for £2,000-2,600.
Mr Mills said: “At this time the empire was ruled jointly by Gratian, his half-brother Valentinian II, and Theodosius so this coin together with an example of each of the other two co-emperors could have provided a donative payment of a Miliarensis celebrating a military victory.”
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