Constantiolus resurfaces in 531, after Belisarius' defeat by the Sassanid Persians at the Battle of Callinicum (19 April 531). Justinian sent Constantiolus to the eastern border, assigning him to investigate the circumstances of the defeat. Constantiolus traveled through Antioch and questioned various Byzantine commanders on the subject. Among them was the "magister officiorum" Hermogenes, who had served under Belisarius in the battle. Constantiolus returned to Constantinople with his findings. His report probably contributed to the end of Belisarius' service as "magister militum per Orientem" and his replacement by Mundus.