Upon returning to his lands, Mundhir learned that a combined Persian-Lakhmid force was preparing another attack against the Ghassanid realm. Immediately he set out to meet them, engaged their army and comprehensively defeated it, before going on to capture the enemy camp. It was to be his last victory. Despite his successes, Mundhir was accused by Maurice of treason during the preceding campaign. Maurice claimed that Mundhir had revealed the Byzantine plan to the Persians, who then proceeded to destroy the bridge over the Euphrates. The chronicler John of Ephesus explicitly calls this assertion a lie, as the Byzantine intentions must have been plain to the Persian commanders. Both Maurice and Mundhir wrote letters to Emperor Tiberius, who tried to reconcile them. Finally, Maurice himself visited Constantinople, where he was able to persuade Tiberius of Mundhir's guilt. The charge of treason is almost universally dismissed by modern historians; Irfan Shahîd says that it probably had more to do with Maurice's dislike of the veteran and militarily successful Arab ruler. This was further compounded by the Byzantines' habitual distrust of the "barbarian" and supposedly innately traitorous Arabs, as well as by Mundhir's staunchly Monophysite faith. Tiberius ordered Mundhir's arrest, and a trap was laid for the Ghassanid king: summoned to Constantinople to answer charges of treason, Mundhir chose his friend, the "curator" Magnus, as his advocate. Magnus was probably a Byzantine, hailing from Huwwarin (Evaria). There he had built a church, and he now called on Mundhir to join him and the patriarch of Antioch Gregory in the dedication ceremony. Mundhir arrived with only a small escort and was arrested by Byzantine troops stationed in secret at the location. He was transported to Constantinople, joined along the way by his wife and three of his children. At the capital, he was treated well by Tiberius, who allowed him a comfortable residence and a subsidy, but denied him an audience. Irfan Shahîd believes that this generous treatment, as well as the fact that he was not brought to trial for his supposed treason, indicate that Tiberius too did not believe the charges, but ordered the arrest chiefly to placate the strong anti-Monophysite faction in the imperial capital. In the meantime, Mundhir's arrest provoked a revolt led by his four sons, especially the eldest, Nu'man, a man described by John of Ephesus as even more capable and warlike than his father.