He had released Demetrius too late to obtain any benefit from the hostile feeling which that prince probably entertained towards his brother.

Had he not released him too soon for his own safety?
Was it not to be feared that the Syrians might rally under one who was their natural leader, might rapidly recover their strength, and renew the struggle for the mastery of Western Asia?
The first thought of the dissatisfied monarch was to hinder the execution of his own project.

Demetrius was on his way to Syria, but had not yet arrived there, or, at any rate, his arrival had not been as yet reported.

Was it not possible to intercept him?
The Parthian king hastily sent out a body of horse, with orders to pursue the Syrian prince at their best speed, and endeavor to capture him before he passed the frontier.

If they succeeded, they were to bring him hack to their master, who would probably have then committed his prisoner to close custody.