This design looks to be crude enough to be a late roman, or maybe its just a spes publicae but any help is appreciated. Thanks.
I would probably guess mid to late 4rth century Roman, but the Emperor's portrait is so heavily encased in patina that I haven't got a clue.
Most likely it is a member of the Constantinian family. http://www.tesorillo.com/aes/088/088i.htm That is about as much as you can id your coin.
