From the two accounts, taken together, we are perhaps entitled to conclude that the entire host did not fall much short of 400,000 men.

This estimate receives confirmation from an independent statement made by Diodorus, with respect to the number who fell in the campaign--a statement of which we shall have to speak later.
The army of Phraates, according to two accounts of it (which, however, seem to represent a single original authority), numbered no more than 120,000.

An attempt which he made to enlist in his service a body of Scythian mercenaries failed, the Scyths being willing to lend their aid, but arriving too late to be of any use.

At the same time a defection of the subject princes deprived the Parthian monarch of contingents which usually swelled his numbers, and threw him upon the support of his own countrymen, chiefly or solely.

Under these circumstances it is more surprising that he was able to collect 120,000 men than that he did not bring into the field a larger number.
The Syrian troops, magnificently appointed and supported by a body of Jews under John Hyrcanus, advanced upon Babylon, receiving on their way the adhesion of many of the Parthian tributaries, who professed themselves disgusted by the arrogance and pride of their masters.
Phraates, on his part, advanced to meet his enemies, and in person or by his generals engaged Antiochus in three battles, but without success.
Antiochus was three times a conqueror.