I suspect it is a Roman Republic denarius. There are many varieties of the type and from what you have left it doesn't seem possible to get more accurate. This is mine for comparison. C Piso L. F. Frugi Denarius Obv:– Laureate head of Apollo right, Fractional mark (two vertical pellets) behind bust and (four pellets) in front? Rev:– Horseman galloping right, holding palm; L PISO FRVGI below, N Pellet above Minted in Rome 90-89 B.C.
@maridvnvm is correct that there are a few different candidates but based on obverse style and apparent lack of rider on reverse I believe this is a denarius of C. Censorinus minted circa 88 BC similar to this: https://www.acsearch.info/search.html?id=1274693 You can see what appears to be the start of the C CE below the horse. I believe corrosion, wear and cleaning have removed the rest.
