The obverse (heads) of this coin has the legend: IMP(erator)ALEXANDER PIVS AVG(vstvs) The reverse (tails) has the legend P(ontifex)M(aximus)TRibunicia) P(otestas)X CO(n)S(ul)III P(ater)P(atriae) which indicates this is a denarius minted in 230 AD by Severus Alexander, who ruled from 222-235 AD. He was the last of the Severan dynasty and considered by many to be the best of the lot. Tolerant, intelligent and decent he was unable to realize his goals for the empire-he was assassinated at the age of 27 by his general Maximinus the Thracian. Here is a great site on Severus Alexander's history and his coinage.