In 208 BC, after his wars with the Ptolemies and his crushing of the rebellion led by Achaeus, Antiochus III the Great turned eastward. He demanded the submission and vassalage of the Bactrian basileus Euthydemus, who himself usurped the throne from the previous dynasty, the Diodotids. After a battle at the River Arius, where he lost his cataphracts, Bactra was besieged for a few years, until Antiochus left, marrying his daughter to Euthydemus afterwards. What if Euthydemus had won a crushing victory there, killing Antiochus and annihilating the royal army? What effect does this have on the Seleucids? Could the Saka and Yuezhi penetrate earlier? Can Bactria survive any longer?