@brit, first welcome to CCF. Second, this coin looks Byzantine to me. If you can post a pic of the other side, we can help narrow down what you have. At that point, I might move your thread over to the ancients subforum so that we can get some expert opinions.
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz