The Secret History of the Court of Justinian by Procopius

According to Wikipedia: Procopius of Caesarea (Latin: Procopius Caesarensis, c. AD 500 – c. AD 565) was a prominent Byzantine scholar from Palestine. 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. He is commonly held to be the last major historian of the ancient world.