Original: Accompanying the general Belisarius in the wars of the Emperor Justinian I, he became the principal historian of the 6th century, writing the Wars of Justinian, the Buildings of Justinian and the celebrated Secret History.
Simplified: He took part in the wars of the Emperor Justinian I, and was the major historian of the 6th century AD, writing the Wars of Justinian, the Buildings of Justinian and the celebrated Secret History.