The city of Rhesaena (also known as Rhesaina or Resaena) was an important ancient town located in the northern extremity of Mesopotamia, near the sources of the Chaboras River (modern Khabur River). It was strategically positioned on the route from Carrhae to Nicephorium, roughly eighty miles from Nisibis and forty from Dara. Today, the site corresponds to Ra’s al-‘Ayn in Syria. Rhesaena was a Roman colony from the time of Emperor Septimius Severus and became part of the Roman province of Mesopotamia Secunda. The city held military significance, housing the garrison of Legio III Parthica Severiana around 197 AD after the annexation of Mesopotamia by Severus.​

Coins minted at Rhesaena generally reflect the city’s military and strategic importance. These coins include bronze (Æ) denominations, such as the Æ15 type certified by NGC you mentioned. The coinage began around 215 AD, likely in preparation for Caracalla’s eastern campaigns. The coins often show typical Roman imperial features, such as a laureate head on the obverse, sometimes supported by martial emblems like eagles. The reverse often includes military symbols and emblems reflecting the legion’s presence and the city’s fortified status.​

Rhesaena’s coinage, including the Caracalla Æ15, is distinctive for its association with the eastern frontier defense system of the Roman Empire. The city’s position and its coins symbolized Rome’s control over Mesopotamia and its conflicts with the Parthian and later Sassanian empires. The bronze coins serve as both currency and propaganda tools asserting imperial strength and the presence of Roman legions in this volatile region.​

Historically, Rhesaena was also a religious center with a bishopric under the jurisdiction of the nearby city of Dara, and it bore the honorary name Theodosiopolis after Emperor Theodosius I, who favored the city. Despite its military and administrative importance, Rhesaena faced repeated attacks and was fortified further under Emperor Justinian. The site witnessed multiple conflicts, including near destruction by Tamerlane’s troops in the 14th century, although it continued to hold religious significance for centuries.​

In summary, the Mesopotamian city of Rhesaena was a strategically significant Roman colony and military stronghold that minted distinctive bronze coins like the Caracalla Æ15. These coins symbolize the city’s role in Roman frontier defense and imperial propaganda. Today, Rhesaena’s ruins lie at Ra’s al-‘Ayn, Syria, a reminder of the city’s rich historical and military heritage within Roman Mesopotamia.​