Ancient Coin Need Id, Celtic Or Greek?

I will try to fix this, but in the future you need to rename the files. There are some special character combinations breaking the display. You can rename them when you upload. Use real words when possible.

@jbuck Thank you very much :)

If you rotate the reverse you will see what looks like a Justinian I (527-565 AD) AE Decanummium





Yours seems even more crude than normal; so maybe unofficial...it's tough to be sure because of the condition.

LOL at the upside-down mintmark!

Unfortunately on the OP's coin the mintmark is off flan. But it's definitely a decanummium, dated RY 30+x, probably 32 or 36 (better pictures would help; it's at 8h on the second pic). With such a large date it's almost certainly of Justinian.

The reverse doesn't look unusually crude to me; those small denominations often looked relatively crude. Unfortunately I can't make any sense of the obverse, which seems to have gotten quite corroded.