Harald was discovered battling on the empire's almost every frontier

One of the interesting facts about Harald Hardrada is that Harald was discovered battling on the empire's almost every frontier. After a few years in Kievan Rus', Harald and his force of around 500 men moved on south to Constantinople (Miklagard), the capital of the Eastern Roman Empire (later known as the Byzantine Empire), probably in 1033 or 1034, where they joined the Varangian Guard. Although the Flateyjarbók claims that Harald initially tried to conceal his royal status, most sources agree that Harald and his troops were well known in the east at the time. While the Varangian Guard was intended to be the emperor's bodyguard, Harald was found fighting on "almost every frontier" of the empire.

He initially saw battle in campaigns against Arab pirates in the Mediterranean Sea, and then in towns in Asia Minor/Anatolia that had backed the pirates. By this time, he had risen to the position of leader over all the Varangians, according to Snorri Sturluson. By 1035, the Byzantines had pushed the Arabs out of Asia Minor to the east and southeast, and Harald participated in campaigns that went as far east as the Tigris and Euphrates rivers in Mesopotamia, where, according to his skald (poet) Þjóðólfr Arnórsson (recounted in the sagas), he participated in the capture of eighty Arab strongholds. Although not maintaining independent command of an army as the sagas claim, it is not impossible that King Harald and the Varangians at times could have been sent off to seize a fortress or town. Harald most likely fought in operations against the Pechenegs during the first four years of Byzantine Emperor Michael IV the Paphlagonian's reign.