In 528, the Persians pressed on from Iberia to capture forts in eastern Lazica. Attempting to remedy the deficiencies revealed by these Persian successes, Justinian reorganised the eastern armies by dividing the command of the "magister militum" of the East in two and appointing a separate "magister militum" of Armenia over the northern portion. The most important Roman initiative on the southern front in 528 was Belisarius's expeditions to Thannuris, where he tried to protect Roman workers, undertaking the construction of a fort right on the frontier. His forces were defeated by Xerxes during the battle of Thannuris and he had to retreat to Dara.