His own army thus amounted to 100,000 men; and, with the Armenian contingent, his entire force would have been 113,000.  It seems that it was his original intention to cross the Euphrates into Mesopotamia, and thus to advance almost in the footsteps of Crassus but when he reached the banks of the river (about midsummer B.C. 37) he found such preparations made to resist him that he abandoned his first design, and, turning northwards, entered Armenia, determined to take advantage of his alliance with Artavasdes, and to attack Parthia with Armenia as the basis of his operations.  Artavasdes gladly received him, and persuaded him, instead of penetrating into Parthia itself, to direct his arms against the territory of a Parthian subject-ally, the king of Media Atropatene, whose territories adjoined Armenia on the southeast.  Artavasdes pointed out that the Median monarch was absent from his own country, having joined his troops to those which Phraates had collected for the defence of Parthia.  His territory therefore would be open to ravage, and even Praaspa, his capital, might prove an easy prey.  The prospect excited Antony, who at once divided his troops, and having given orders to Oppius Statianus to follow him leisurely with the more unwieldy part of the army, the baggage-train, and the siege batteries, proceeded himself by forced marches to Praaspa with all the calvary and the infantry of the better class.  This town was situated at the distance of nearly three hundred miles from the Armenian frontier; but the way to it lay through well-cultivated plains, where food and water were abundant.  Antony performed the march without difficulty and at once invested the place.  The walls were strong, and the defenders numerous, so that he made little impression; and when the Median king returned, accompanied by his Parthian suzerain, to the defence of his country, the capital seemed in so little danger that it was resolved to direct the first attack on Statianus, who had not yet joined his chief.  A most successful onslaught was made on this officer, who was surprised, defeated, and slain.  Ten thousand Romans fell in the battle, and all the baggage-wagons and engines of war were taken.  A still worse result of the defeat was the desertion of Aitavasdes, who, regarding the case of the Romans as desperate, drew off his troops, and left Antony to his own resources.

The Roman general now found himself in great difficulties.  He had exhausted the immediate neighborhood of Praaspa, and was obliged to send his foraging-parties on distant expeditions, where, being beyond the reach of his protection, they were attacked and cut to pieces by the enemy.  He had lost his siege-train, and found it impossible to construct another.  Such works as he attempted suffered through the sallies of the besieged:  and in some of these his soldiers behaved so ill that he was forced to punish their cowardice by decimation.  His supplies failed, and he had to feed his troops on barley instead of wheat.