The Makeup of the Roman Army That Came Against Jerusalem.

6. Thus did John hope to be too hard for his enemies by these engines constructed by his impiety; but God himself demonstrated that his pains would prove of no use to him, by bringing the Romans upon him, before he had reared any of his towers; for Titus, when he had gotten together part of his forces about him, and had ordered the rest to meet him at Jerusalem, marched out of Cesarea. 

He had with him those three legions that had accompanied his father when he laid Judea waste, together with that twelfth legion which had been formerly beaten with Cestius; which legion, as it was otherwise remarkable for its valor, so did it march on now with greater alacrity to avenge themselves on the Jews, as remembering what they had formerly suffered from them. Of these legions he ordered the fifth to meet him, by going through Emmaus, and the tenth to go up by Jericho; he also moved himself, together with the rest; besides whom, marched those auxiliaries that came from the kings, being now more in number than before, together with a considerable number that came to his assistance from Syria. 

Those also that had been selected out of these four legions, and sent with Mucianus to Italy, had their places filled up out of these soldiers that came out of Egypt with Titus; who were two thousand men, chosen out of the armies at Alexandria. There followed him also three thousand drawn from those that guarded the river Euphrates ; as also there came Tiberius Alexander, who was a friend of his, most valuable, both for his good-will to him, and for his prudence. He had formerly been governor of Alexandria, but was now thought worthy to be general of the army [under Titus]. 

The reason of this was, that he had been the first who encouraged Vespasian very lately to accept this his new dominion, and joined himself to him with great fidelity, when things were uncertain, and fortune had not yet declared for him. He also followed Titus as a counselor, very useful to him in this war, both by his age and skill in such affairs.    Book V, Chapter I, Section 6 (Entire)