Looks like a late Roman votive issue. Pretty common, and most likely from Constantius II or another one of Constantine's sons. I cannot make out the legend.
Btw, most likely from about 330-350ad timeframe. I am sure others here who know more about these than I can be of more help.
I think it's most likely Valentinian II, about 383-387, unfortunately w/o mintmark it's impossible to have a positive id.