A formal mutiny compelled the general to order a retreat, which he effected with his usual skill. When he had safely reached Mesopotamia where the season still permitted farther operations, Lucullus crossed the Tigris, and threw himself with the mass of his army on Nisibis, the last city that here remained to the Armenians. The great-king, rendered wiser by the experience acquired before Tigranocerta, left the city to itself: notwithstanding its brave defence it was stormed in a dark, rainy night by the besiegers, and the army of Lucullus found there booty not less rich and winter- quarters not less comfortable than the year before in Tigranocerta. Conflicts in Pontus and at Tigranocerta But, meanwhile, the whole weight of the enemy's offensive fell on the weak Roman divisions left behind in Pontus and in Armenia. Tigranes compelled the Roman commander of the latter corps, Lucius Fannius--the same who had formerly been the medium of communication between Sertorius and Mithradates (18)--to throw himself into a fortress, and kept him beleaguered there. Mithradates advanced into Pontus with 4000 Armenian horsemen and 4000 of his own, and as liberator and avenger summoned the nation to rise against the common foe. All joined him; the scattered Roman soldiers were everywhere seized and put to death: when Hadrianus, the Roman commandant in Pontus,(19) led his troops against him, the former mercenaries of the king and the numerous natives of Pontus following the army as slaves made common cause with the enemy. For two successive days the unequal conflict lasted; it was only the circumstance that the king after receiving two wounds had to be carried off from the field of battle, which gave the Roman commander the opportunity of breaking off the virtually lost battle, and throwing himself with the small remnant of his troops into Cabira. Another of Lucullus' lieutenants who accidentally came into this region, the resolute Triarius, again gathered round him a body of troops and fought a successful engagement with the king; but he was much too weak to expel him afresh from Pontic soil, and had to acquiesce while the king took up winter-quarters in Comana. Farther Retreat to Pontus