On the reverse of the quadriga types, Constantine is depicted wearing robes, like a burial shroud. On some coins, it is not so clear what he is wearing (see last picture for some assorted styles). On this example it looks like he is mummified. Maybe this was still a fairly common practice in Antioch, or perhaps the engraver thought it was proper, or he just depicted the shroud tightly wrapped around Constantine...or maybe it just looks like a mummy to me!