Identification of a Ancient Coin. Probably a Roman Coin!?

Hello please I need help with this old coin. Probably a Roman coin. Bronze, about 30 mm and weighs 8.5 grams.
Emperor's face and part of the legend on the obverse visible, but I couldn't decipher much, from one angle it looks like Greek letters with an example of two omegas and a sigma letters, but from another angle you see Latin letters like E and S.
On the reverse, just visible a circle on the edge of the coin and a letter P to the left and almost invisible shadows of other letters.
Thanks for helping.

New informations after intense research. Definitively a PAX reverse type!

Problem is both COS and PAX are common on Roman coins so doesn't offer much to work with. The random S in the middle is paired with a C on the other side meaning Senatus consultum. At 30mm and 8,5g it's most likely a sestertius, my guess would be late 1st early 2nd century. Wear can explain why it's underweight. Judging from portrait alone I'd say Vespasian or Titus however without part of the obverse legend being readable I don't think we can ever be sure. I doubt there are any Greek letters on the coins since that was usually found on provincial coins and those didn't have Latin alphabet on them or carried the SC.

AVG just means Augustus and is also common on Roman coins. The more I look at the portrait the more it looks like Philippus I however, I repeat, this is just guessing and without being able to read the legend we can never be sure.

Citeer: "cro321"​AVG just means Augustus and is also common on Roman coins. The more I look at the portrait the more it looks like Philippus I however, I repeat, this is just guessing and without being able to read the legend we can never be sure.

Thank you, I'll try to decipher something else from the legend and I'll send it here.

Citeer: "cro321"​Problem is both COS and PAX are common on Roman coins so doesn't offer much to work with. The random S in the middle is paired with a C on the other side meaning Senatus consultum. At 30mm and 8,5g it's most likely a sestertius, my guess would be late 1st early 2nd century. Wear can explain why it's underweight. Judging from portrait alone I'd say Vespasian or Titus however without part of the obverse legend being readable I don't think we can ever be sure. I doubt there are any Greek letters on the coins since that was usually found on provincial coins and those didn't have Latin alphabet on them or carried the SC.

​ Oh yes I get it, thank you very much for the information. I'll try to decipher something else in the legend and put it here.

WOW! New discovery: probable POSTVMUS bronze coin. All marked letters make sense after looking from many angles in daylight.
And it's even more possible, since since I picked up the coin, I've seen a kind of radiated crown.

Radiate crown would make it a dupondius, took a quick look at WildWind, this comes close with a PAX SC reverse but doesn't have the COS on the obverse:

Citeer: "cro321"​Radiate crown would make it a dupondius, took a quick look at WildWind, this comes close with a PAX SC reverse but doesn't have the COS on the obverse:
​
​

​ Yes, it doesn't even have COS, after looking at it better it was actually the end of the Postumus name. I will look for something similar in WildWind. Thanks.

After looking for a while, I came to the conclusion that my coin beats almost 100% all the details equal to the dupondius of the link below:
http://numismatics.org/ocre/id/ric.5.post.218
But, although I know that weight and diameter are very variable in Roman coins, I thought about the possibility of also being a sestertius, whose legends match my coin, but there are no photos for me to compare:
http://numismatics.org/ocre/id/ric.5.post.153
What do you think!? Thanks!
And finally identifying the coin, can I add it inside which issuer!? Gallic Empire!? This issuer still only has Postumus's antoninianus, no dupondius or sestertius so far. Thank you all.