6 days ago
It should be a Byzantine anonymous follis coin. The Byzantine Empire would be a 'sort of' continuation of the Roman Empire. Such a coin isn't that rare, so I would say it be roughly valued around $15-35 USD.
It would depict Christ on one side, and on the other side, a cross.
You might not want to expose that coin to water, as from what I can see, that green colored small patch might be corrosion called bronze disease, where it would corrode the coin if it grows more when water is in contact with it.