The truce established in the early summer, when Volagases sent his envoys to Nero, expired in the autumn, on their return without a definite reply; and the Roman commanders at once took the offensive and entered upon an autumn campaign, the second within the space of a year.  Corbulo crossed the Euphrates in the face of a large Parthian army, which he forced to retire from the eastern bank of the river by means of military engines worked from ships anchored in mid-stream.  He then advanced and occupied a strong position in the hills at a little distance from the river, where he caused his legions to construct an entrenched camp.  Paetus, on his part, entered Armenia from Cappadocia with two legions, and, passing the Taurus range, ravaged a large extent of country; winter, however, approaching, and the enemy nowhere appearing in force, he led back his troops across the mountains, and, regarding the campaign as finished, wrote a despatch to Nero boasting of his successes, sent one of his three legions to winter in Pontus, and placed the other two in quarters between the Taurus and the Euphrates, at the same time granting furloughs to as many of the soldiers as chose to apply for them.  A large number took advantage of his liberality, preferring no doubt the pleasures and amusements of the Syrian and Cappadocian cities to the hardships of a winter in the Armenian highlands.  While matters were in this position Paetus suddenly heard that Volagases was advancing against him.  As once before at an important crisis, so now with the prospect of Armenia as the prize of victory, the Parthians defied the severities of winter and commenced a campaign when their enemy regarded the season for war as over.  In this crisis Paetus exhibited an entire unfitness for command.  First, he resolved to remain on the defensive in his camp; then, affecting to despise the protection of ramparts and ditches, he gave the order to advance and meet the enemy; finally, after losing a few scouts whom he had sent forward, he hastily retreated and resumed his old position, but at the same time unwisely detached three thousand of his best foot to block the pass of Taurus, through which Volagases was advancing.  After some hesitation he was induced to make Corbulo acquainted with his position; but the message which he sent merely stated that he was expecting to be attacked.  Corbulo was in no hurry to proceed to his relief, preferring to appear upon the scene at the last moment, when he would be hailed as a savior.

Volagases, meanwhile, continued his march.  The small force left by Paetus to block his progress was easily overpowered, and for the most part destroyed.  The castle of Arsamosata, where Paetus had placed his wife and child, and the fortified camp of the legions, were besieged.  The Romans were challenged to a battle, but dared not show themselves outside their entrenchments.  Having no confidence in their leader, the legionaries despaired and began openly to talk