Calonymus was probably a native of Alexandria, capital of the Diocese of Egypt. In 533, he was assigned as the sole commander of the Byzantine navy during the Vandalic War. Its mission was to transport the troops of Belisarius to the Vandal Kingdom of North Africa. Procopius reports in detail the naval force assembled: "And for the whole force five hundred ships were required, no one of which was able to carry more than fifty thousand medimni, nor any one less than three thousand. And in all the vessels together there were thirty thousand sailors, Egyptians and Ionians for the most part, and Cilicians, and one commander was appointed over all the ships, Calonymus of Alexandria. And they had also ships of war prepared as for sea-fighting, to the number of ninety-two, and they were single-banked ships covered by decks, in order that the men rowing them might if possible not be exposed to the bolts of the enemy. Such boats are called "dromones" by those of the present time; for they are able to attain a great speed. In these sailed two thousand men of Byzantium, who were all rowers as well as fighting men; for there was not a single superfluous man among them."