In 531, Mundus was briefly "magister militum per Orientem", replacing Belisarius after his failure at Callinicum, but it seems that Mundus never actually traveled to the East to assume that command. In January 532, he was again appointed commander of the Illyrian forces. In the same month, he happened to be in Constantinople with a force of Heruli mercenaries when the Nika riots broke out. Mundus remained loyal to Justinian and, along with Belisarius, was responsible for the massacre of the supporters of Hypatius in the Hippodrome and thus the reassertion of imperial control.