Mundhir learns upon returning to his lands that a combined Persian-Lakhmid force is preparing another attack against the Ghassanid realm.

Immediately he sets out to meet them, engages their army and comprehensively defeats it, before going on to capture the enemy camp.

It is to be his last victory.

Despite his successes, Mundhir is accused by Maurice of treason during the preceding campaign.

Maurice claims that Mundhir had revealed the imperial 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 write letters to Emperor Tiberius, who tries to reconcile them.

Finally, Maurice himself visits Constantinople, where he is 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 is further compounded by the Empire's habitual distrust of the "barbarian" and supposedly innately traitorous Arabs, as well as by Mundhir's staunchly Monophysite faith.

Tiberius orders Mundhir's arrest, and a trap is laid for the Ghassanid king: summoned to Constantinople to answer charges of treason, Mundhir chooses his friend, the curator Magnus, a prominent aristocratic figure and close ally to emperors Justin II and Tiberius II, as his advocate.

Magnus owns property in Evaria (present Huwwarin) and finances many of its construction projects.

Here he has built a church as well as a wall surrounding it, and now calls on Mundhir to join him and the patriarch of Antioch Gregory in the dedication ceremony.

Mundhir arrives with only a small escort and is arrested by imperial troops stationed in secret at the location.

He is transported to Constantinople, joined along the way by his wife and three of his children.

Mundhir's arrest provokes a revolt led by his four sons, especially the eldest, al-Nu'man, a man described by John of Ephesus as even more capable and warlike than his father.

Following Magnus's departure from Huwwarin, al-Nu'man's troops raid and thoroughly plunder the city, slaying a number of its residents.