here's an interesting article about the Killingholme treasure:
"Old bottle caps and rusty nails aren’t the only things metal detectorists can find. Sometimes amateur treasure hunters make a big haul. Such was the case with the Killingholme Treasure, a collection of over 4000 Roman coins minted by the Roman Empire almost 1700 years ago."
A coin of Constantine I from the Killingholme hoard.