The Seleucid kingdom, prevented from retaking the Parthian lands it once controlled, begins to rapidly disintegrate.

The defeat of Antiochus has finally ended Seleucid dominion over the countries east of the Euphrates River, and marks the beginning of small principalities in both the north and south of Mesopotamia.

In Mesene (also called Characene, Persian Meshan), a Seleucid satrap with an Iranian name, Hyspaosines (also called Aspasine, or Spasines, who reigns from 127 BCE to about 121 BCE, refortifies Antiochia, a town originally founded by Alexander the Great near the junction of the Eulaeus (Karun) and Tigris rivers, and calls it Spasinou Charax (“Fort of Spasines”).

…conquers Characene, overstriking coins of Hyspaosines and driving him from his capital in 122 or 121.

Trajan continues southward to the Persian Gulf, receiving the submission of Athambelus, the ruler of Charax, whence he declares Babylon a new province of the Empire, sends the Senate a laureled letter declaring the war to be at a close and bemoaning that he is too old to go on any further and repeat the conquests of Alexander the Great.

A province of Assyria is also proclaimed, apparently covering the territory of Adiabene, as well as some measures seem to have been considered about the fiscal administration of the Indian trade.

However, as Trajan leaves the Persian Gulf for Babylon—where he intends to offer sacrifice to Alexander in the house where he had died in 323 BCE—a sudden outburst of Parthian resistance, led by a nephew of the Parthian king, Sanatruces, imperils Roman positions in Mesopotamia and Armenia, something Trajan seeks to deal with by forsaking direct Roman rule in Parthia proper, at least partially.