So soon as the season allowed, the Roman troops crossed the frontier of Pontus. There they were opposed by king Mithradates with 30,000 infantry and 3000 cavalry. Left in the lurch by his allies and attacked by Rome with reinforced power and energy, he made an attempt to procure peace; but he would hear nothing of the unconditional submission which Pompeius demanded - what worse could the most unsuccessful campaign bring to him? That he might not expose his army, mostly archers and horsemen, to the formidable shock of the Roman infantry of the line, he slowly retired before the enemy, and compelled the Romans to follow him in his various cross-marches; making a stand at the same time, wherever there was opportunity, with his superior cavalry against that of the enemy, and occasioning no small hardship to the Romans by impeding their supplies. At length Pompeius in his impatience desisted from following the Pontic army, and, letting the king alone, proceeded to subdue the land; he marched to the upper Euphrates, crossed it, and entered the eastern provinces of the Pontic empire.

But Mithradates followed along the left bank of the Euphrates, and when he had arrived in the Anaitic or Acilisenian province, he intercepted the route of the Romans at the castle of Dasteira, which was strong and well provided with water, and from which with his light troops he commanded the plain. Pompeius, still wanting the Cilician legions and not strong enough to maintain himself in this position without them, had to retire over the Euphrates and to seek protection from the cavalry and archers of the king in the wooded ground of Pontic Armenia extensively intersected by rocky ravines and deep valleys. It was not till the troops from Cilicia arrived and rendered it possible to resume the offensive with a superiority of force, that Pompeius again advanced, invested the camp of the king with a chain of posts of almost eighteen miles in length, and kept him formally blockaded there, while the Roman detachments scoured the country far and wide. The distress in the Pontic camp was great; the draught animals even had to be killed; at length after remaining for forty-five days the king caused his sick and wounded, whom he could not save and was unwilling to leave in the hands of the enemy, to be put to death by his own troops, and departed during the night with the utmost secrecy towards the east. Cautiously Pompeius followed through the unknown land: the march was now approaching the boundary which separated the dominions of Mithradates and Tigranes. When the Roman general perceived that Mithradates intended not to bring the contest to a decision within his own territory, but to draw the enemy away after him into the far distant regions of the east, he determined not to permit this.

The two armies lay close to each other. During the rest at noon the Roman army set out without the enemy observing the movement, made a circuit, and occupied the heights, which lay in front and commanded a defile to be passed by the enemy, on the southern bank of the river Lycus (Jeschil-Irmak) not far from the modern Enderes, at the point where Nicopolis was afterwards built. The following morning the Pontic troops broke up in their usual manner, and, supposing that the enemy was as hitherto behind them, after, accomplishing the day's march they pitched their camp in the very valley whose encircling heights the Romans had occupied. Suddenly in the silence of the night there sounded all around them the dreaded battle-cry of the legions, and missiles from all sides poured on the Asiatic host, in which soldiers and camp-followers, chariots, horses, and camels jostled each other; and amidst the dense throng, notwithstanding the darkness, not a missile failed to take effect. When the Romans had expended their darts, they charged down from the heights on the masses which had now become visible by the light of the newly-risen moon, and which were abandoned to them almost defenceless; those that did not fall by the steel of the enemy were trodden down in the fearful pressure under the hoofs and wheels. It was the last battle-field on which the gray-haired king fought with the Romans. With three attendants - two of his horsemen, and a concubine who was accustomed to follow him in male attire and to fight bravely by his side - he made his escape thence to the fortress of Sinoria, whither a portion of his trusty followers found their way to him. He divided among them his treasures preserved there, 6000 talents of gold (1,400,000 pounds); furnished them and himself with poison; and hastened with the band that was left to him up the Euphrates to unite with his ally, the great-king of Armenia.

This hope likewise was vain; the alliance, on the faith of which Mithradates took the route for Armenia, already by that time existed no longer. During the conflicts between Mithradates and Pompeius just narrated, the king of the Parthians, yielding to the urgency of the Romans and above all of the exiled Armenian prince, had invaded the kingdom of Tigranes by force of arms, and had compelled him to withdraw into the inaccessible mountains.

The invading army began even the siege of the capital Artaxata; but, on its becoming protracted, king Phraates took his departure with the greater portion of his troops; whereupon Tigranes overpowered the Parthian corps left behind and the Armenian emigrants led by his son, and re-established his dominion throughout the kingdom Naturally, however, the king was under such circumstances little inclined to fight with the freshly-victorious Romans, and least of all to sacrifice himself for Mithradates; whom he trusted less than ever, since information had reached him that his rebellious son intended to betake himself to his grandfather. So he entered into negotiations with the Romans for a separate peace; but he did not wait for the conclusion of the treaty to break off the alliance which linked him to Mithradates. The latter, when he had arrived at the frontier of Armenia, was doomed to learn that the great-king Tigranes had set a price of 100 talents (24,000 pounds) on his head, had arrested his envoys, and had delivered them to the Romans. King Mithradates saw his kingdom in the hands of the enemy, and his allies on the point of coming to an agreement with them; it was not possible to continue the war; he might deem himself fortunate, if he succeeded in effecting his escape along the eastern and northern shores of the Black Sea, in perhaps dislodging his son Machares - who had revolted and entered into connection with the Romans[6] - once more from the Bosporan kingdom, and in finding on the Maeotis a fresh soil for fresh projects. So he turned northward. When the king in his flight had crossed the Phasis, the ancient boundary of Asia Minor, Pompeius for the time discontinued his pursuit; but instead of returning to the region of the sources of the Euphrates, he turned aside into the region of the Araxes to settle matters with Tigranes.

Almost without meeting resistance he arrived in the region of Artaxata (not far from Erivan) and pitched his camp thirteen miles from the city. There he was met by the son of the great-king, who hoped after the fall of his father to receive the Armenian diadem from the hand of the Romans, and therefore had endeavoured in every way to prevent the conclusion of the treaty between his father and the Romans. The great-king was only the more resolved to purchase peace at any price. On horseback and without his purple robe, but adorned with the royal diadem and the royal turban, he appeared at the gate of the Roman camp and desired to be conducted to the presence of the Roman general. After having given up at the bidding of the lictors, as the regulations of the Roman camp required, his horse and his sword, he threw himself in barbarian fashion at the feet of the proconsul and in token of unconditional surrender placed the diadem and tiara in his hands. Pompeius, highly delighted at a victory which cost nothing, raised up the humbled king of kings, invested him again with the insignia of his dignity, and dictated the peace. Besides a payment of; 1,400,000 pounds (6000 talents) to the war-chest and a present to the soldiers, out of which each of them received 50 denarii(2 pounds 2 shillings), the king ceded all the conquests which he had made, not merely his Phoenician, Syrian, Cilician, and Cappadocian possessions, but also Sophene and Corduene on the right bank of the Euphrates; he was again restricted to Armenia proper, and his position of great-king was, of course, at an end.