Al-Harith leads a five thousand-strong Arab contingent in the Battle of Callinicum, in which twenty thousand men under command of Belisarius are defeated by Persian and Lakhmid forces in 531.

Belisarius withdraws his exhausted army to Sura on the Euphrates, where he holds his ground against repeated Persian assaults.

During the summer of the same year, the Romans capture some forts in Armenia, and effectively repulse a Persian offensive, while the Persian capture two forts in eastern Lazica.

Immediately after the failure at Callinicum, the Persians and Romans negotiate without success.

The Roman failure at Callinicum is followed by a commission of inquiry, the result of which is the dismissal of Belisarius from his post.

Procopius, a source hostile to the Ghassanid ruler, states that the Arabs, stationed on the Roman right, betrayed the Romans and fled, costing them the battle.

John Malalas, however, whose record is generally more reliable, reports that while some Arabs indeed fled, Harith stood firm.

The charge of treason leveled by Procopius against Harith seems to be further undermined by the fact that, unlike Belisarius, he is retained in command and is active in operations around Martyropolis later in the year.