Thilutha is described as stronger than Anathan, and indeed as almost impregnable.

Julian felt that he could not attack it with any hope of success, and therefore once more submitted to use persuasion.

But the garrison, feeling themselves secure, rejected his overtures; they would wait, they said, and see which party was superior in the approaching conflict, and would then attach themselves to the victors.

Meanwhile, if unmolested by the invader, they would not interfere with his advance, but would maintain a neutral attitude.
Julian had to determine whether he would act in the spirit of an Alexander, and, rejecting with disdain all compromise, compel by force of arms an entire submission, or whether he would take lower ground, accept the offer made to him, and be content to leave in his rear a certain number of unconquered fortresses.

He decided that prudence required him to take the latter course, and left Thilutha unassailed.
It is not surprising that, having admitted the assumption of a neutral position by one town, he was forced to extend the permission to others, and so to allow the Euphrates route to remain, practically, in the hands of the Persians.
A.five days' march from Thilutha brought the army to a point opposite Diacira, or Hit, a town of ancient repute, and one which happened to be well provided with stores and provisions.