Antiquities of the Jews And a History of the Jewish Wars, etc.
Josephus was a priest, a soldier, and a scholar. He was born Joseph ben Mattathias in Jerusalem in 37 CE. During the Jewish revolt he was taken prisoner by Vespasian, Josephus presented himself as a prophet. Noting that the war had been propelled by an ancient oracle that foretold a world ruler would arise from Judaea, Josephus asserted that this referred to Vespasian, who was destined to become Emperor of Rome. Intrigued, Vespasian spared his life. When this prophecy came true, and Vespasian became Emperor, he rewarded Josephus handsomely, freeing him from his chains and eventually adopting him into his family, the Flavians. Josephus thus became Flavius Josephus.
During the remainder of the war, Josephus assisted the Roman commander Titus, Vespasian's son, with understanding the Jewish nation and in negotiating with the revolutionaries. Called a traitor, he was unable to persuade the defenders of Jerusalem to surrender to the Roman siege, and instead became a witness to the destruction of the city and the Holy Temple. Living at the Flavian court in Rome, Josephus undertook to write a history of the war he had witnessed. The work, while apparently factually correct, also served to flatter his patron and to warn other provinces against the folly of opposing the Romans. It was published a few years after the end of the war, in about 78 CE.