Not a lot to go on - weight and diameter might help a little - The "S" and line on the reverse make me think of a 5th century monogram...maybe something like this: Leo I, AD 457-474, AE nummus no legible legend, diademed head of Leo I right / Monogram of Leo https://www.acsearch.info/search.html?id=3711298 or more here: http://www.wildwinds.com/coins/ric/leo_I/t.html Good luck.
Perhaps it is an extremely late Roman bronze... so late that into the Byzantine era . In Byzantine coinage, in some series a large I on the reverse indicates the denomination of 10 nummi (decanummium). Big disclaimer: I am not very knowledgeable of Byzantine coins, and I can't even tell if that really is an I, and you never told us the size and weight. A reminder of how to get maximum feedback when asking the forum members to identify a coin for you: https://www.cointalk.com/threads/ancient-coins-beginners’-faq-thread.324858/#post-3206493
This thread is a double post. I already identified it a Marcian https://www.cointalk.com/threads/help-id-late-roman.339120/#post-3531127
