This coin has been passed down from my uncle to me, he found this coin in a field in France when he was a child. Can someone tell me what coin it is and how much its worth?
It's a coin of the emperor Maximianus struck in the summer of 307 AD in the London mint. The denomination is usually called a follis by most collectors and a nummus by more academic sources, but it's unclear what it was called in the ancient world. The standard reference for these coins is the sixth volume of Roman Imperial Coins, and this one is the entry RIC VI London 90. Comparing to the examples on VCoins right now, I'd say that this is probably worth somewhere around $30 in this shape, though you might want a second opinion on that.
I believe this one is RIC VI 85 - the difference between the two types is the headdress that Genius wears. On 85 it is a modius, on 90 a tower. See the OP's other thread: http://www.cointalk.com/t203809/
