The long campaigning and hardships that Lucullus' troops had endured for years, combined with a perceived lack of reward in the form of plunder, led to successive mutinies among the legions in 68–67. Frustrated by the rough terrain of Northern Armenia and seeing the worsening morale of his troops, Lucullus moved back south and put Nisibis under siege. Tigranes concluded (wrongly) that Nisibis would hold out and sought to regain those parts of Armenia that the Romans had captured. Despite his continuous success in battle, Lucullus could still not capture either one of the monarchs. With Lucullus' troops now refusing to obey his commands, but agreeing to defend positions from attack, the Senate sent Pompey to recall Lucullus to Rome and take over his command.