XLI. As Antonius was intending to lead the troops back by the same road, which was through a plain country without trees, a man, by nation a Mardian,[412] who was well acquainted with the Parthian habits, and had already shown himself faithful to the Romans in the battle at the waggons, came up to Antonius and advised him in his flight to keep to the mountains on his right, and not to expose a force, in heavy armour and encumbered, to so numerous a cavalry and to the arrows in bare and open tracts, which was the very thing that Phraates designed when he induced him by friendly terms to raise the siege; and that he would lead them a shorter road, where he would find a better supply of necessaries. Antonius on hearing this deliberated; he did not wish to appear to distrust the Parthians after the truce, yet as he approved of the shorter road, and the line of march being along inhabited villages, he asked the Mardian for a pledge of his fidelity. The Mardian offered himself to be put in chains until he should place the army in Armenia; and he was put in chains, and he conducted them for two days without their meeting with any opposition. On the third day, when Antonius had completely ceased to think of the Parthians, and was advancing in a careless way by reason of his confidence, the Mardian observed that an embankment against the overflowing of a river had been recently broken, and that the stream was flowing in a great current on the road by which they had to pass, and he knew that the Parthians had done this with the intention of making the river an obstacle to the Roman march by the difficulty and delay that it would occasion; and he bade Antonius look out and be on his guard, as the enemy was near. Just while he was placing the heavy-armed men in order, and taking measures for the javelin-men and slingers to make an attack through their ranks upon the enemy, the Parthians appeared and rode round them with the design of encircling the Romans and putting them in disorder on all sides. The light-armed troops made a sally against them, and the Parthians, after inflicting some wounds with their arrows and receiving as many from the leaden bullets[413] and javelins of the Romans, retreated. The Parthians then commenced a second attack, which continued until the Celtæ in a mass drove their horses against them and dispersed them; and the Parthians showed themselves no more on that day.