According to Josephus in War 4.11.5, Titus assembled the troops for the siege of Jerusalem at Caesarea, which is near Mount Carmel, a possible location of the mount referred to in the word Armageddon (from Har -or Mount of- Megiddo). since it's at the head of the Jezreel Valley, which is also called the Valley of Megiddo.
... Vespasian ...sent his son Titus, with a select part of his army, to destroy Jerusalem ... to Caesarea, having taken a resolution to gather all his other forces together at that place.
And in War 5.1.1, Josephus says that the sedition in Jerusalem split into three factions, which he calls "the effect of divine justice," since it contributed to the destruction of the city by the Romans.
... it so happened that the sedition at Jerusalem was revived, and parted into three factions, and that one faction fought against the other; which partition in such evil cases may be said to be a good thing, and the effect of divine justice. Now as to the attack the zealots made upon the people, and which I esteem the beginning of the city's destruction, it hath been already explained after an accurate manner; as also whence it arose, and to how great a mischief it was increased. But for the present sedition, one should not mistake if he called it a sedition begotten by another sedition, and to be like a wild beast grown mad, which, for want of food from abroad, fell now upon eating its own flesh.
Then in War 5.6.3 Josephus says the stones that were catapulted into Jerusalem weighed a talent, which is about a hundred pounds (cf. Rev. 16:21: "And great hailstones weighing almost a hundred pounds each rained down on them from above. And men cursed God for the plague of hail, because it was so horrendous").
Now the stones that were cast were of the weight of a talent, and were carried two furlongs and further. The blow they gave was no way to be sustained, not only by those that stood first in the way, but by those that were beyond them for a great space. As for the Jews, they at first watched the coming of the stone, for it was of a white color, and could therefore not only be perceived by the great noise it made, but could be seen also before it came by its brightness; accordingly the watchmen that sat upon the towers gave them notice when the engine was let go, and the stone came from it, and cried out aloud, in their own country language, THE STONE COMETH so those that were in its way stood off, and threw themselves down upon the ground; by which means, and by their thus guarding themselves, the stone fell down and did them no harm. But the Romans contrived how to prevent that by blacking the stone, who then could aim at them with success, when the stone was not discerned beforehand, as it had been till then; and so they destroyed many of them at one blow.
This all sounds like Rev. 16 to me, and my guess is that this could be because whoever wrote Revelation experienced the 66-70 CE war or knew people who had, or they got these details from Josephus or some other account of the war.