Rhesaena, or rather Rhesaina, a city of Mesopotamia, situate on the declivity of Mount Masius, near the river Chabora at its confluence with the river Euphrates, not very far from Carrhae, and close upon the eastern frontier of the Roman Empire. This place was later called Theodosiopolis, and is presently Ras-al-ain (Asiatic Turkey, province of Diarbekir). It was made a colony by Septimius Severus, as is indicated by its assumed surname Septimias, adopted from that of Severus's family.
Near Rhesaena, the Persian King was finally defeated and his army put to flight by Gordianus Pius (Gordian III).
Old writers furnish no particulars respecting this Mesopotamian town; but its coins, which take their date from the reign of Hadrian, form in this respect a supplemental monument to history. They consist of Greek Imperial of Caracalla; and of Roman Provincial successively dedicated to Severus Alexander, Trajan Decius, Herennia Etruscilla, and Herennius. These later have Greek legends with some few words in Latin. For example, on a rare second brass struck in honour of Severus Alexander, the legend PHCAINHCIWN, Rhesainesiorum, accomanied by the type of a colonist at plough with oxen, together with a vexillum, upon which is inscribed LEG III GAL.