Roman Coin, Delmatius?

Constantius II. The CONSTANTI part is pretty clear. How did you get Delmatius?

Yes all emperors look pretty much the same in the late empire. You can narrow it down a bit by the style, since this style (diademed with ties at the back, instead of laureate, radiate or in a helmet) tends to be from the mid-300s onwards. But really you have to go by the legend (if it's there) and the reverse type.

Even then, with 'Constanti' it could've been Constantine II or Constantius II (or even Constantine I, but the style rules him out). At the end of the obverse legend you can see 'AVG' for Augustus, and Constantine II's legends with this reverse only end IVN NOB C (for Younger Noble Caesar). So it has to be Constantius II.

This is a very common reverse, so it helps you have a bit of the mintmark. The 'T' means it has to be Thessalonica (SMTS/A or Epsilon) or Trier (TRP/S). I'm guessing this is Thessalonica.

The crown is rosette diademed, and there is no palm branch, so I'd say it's RIC VIII Thessalonica 99 http://numismatics.org/ocre/id/ric.8.thes.99

This reverse type was issued after the death of Constantine I and Constantine II, so it was only struck for Constans and Constantius II.