I have half a roman coin cleanly cut(microscope) it also has an M within a square stamped over it.?

The coin is bronze.The inscription unclear possibly part MIUS.The M within a square has been punched over the coin after the clean split with V shaped chisel(Microscope).I know coin splitting has been used in USA i.e. QUARTER...BIT.. were the ROMANS coin splitters too..I could understand this with precious metal,,GOLD/SILVER but Bronze?