Revelation 9:16

And the number of the army of the horsemen
This shows that the four angels before mentioned were men, and design generals of armies, or armies of men, even of horsemen; and manifestly point at the Turks, who were not only originally Persians, and had their name, as some say ^F5, from Turca in Persia, and (vrp) , from whence the Persians have their name, signifies an horseman; but the armies of the Turks chiefly consisted of horse, and what for show and for use, they had generally double the number of horses and mules as of men ^F6; and they are very good horsemen, and very dextrous at leaping on and off ^F7; and the horse's tail is still carried before the general, and principal officers, as an ensign expressive of their military exploits, and showing where their main strength lies. And the number of this mighty army, it is said,

[were] two hundred thousand thousand;
or "two myriads of myriads"; two hundred millions, or twenty thousand brigades of ten thousand each; that is, a very large and prodigious number, almost infinite and incredible, like the army of Gog and Magog, as the sand of the sea, ( Revelation 20:8 ) . The Turks used to bring, and still do bring vast armies into the field: in the year 1396, Bajazet, with three hundred thousand men, fell upon sixty thousand Christians, killed twenty thousand of them, and lost sixty thousand of his own: against him afterward, in the year 1397, came Tamerlane the Tartar, with four hundred thousand horse, and six hundred thousand foot, and having killed two hundred thousand Turks, took Bajazet prisoner, and carried him about in a cage, in golden chains. In the year 1438, Amurath entered into Pannonia, with three hundred thousand horsemen: and in the year 1453, Mahomet took Constantinople with the like number ^F8; yea, it is said, that the army at the siege of that city consisted of forty myriads, or four hundred thousand men ^F9. It is reported, that the great Turk contemptuously sent to the emperor of the Romans a camel, or a dromedary, loaden with wheat, with this vow by a message, that he should bring against him as many fighting men as there were grains of wheat therein ^F11. And it is related ^F12, that when Ladislaus, king of Hungary, went out against Amurath with four and twenty thousand horse, Dracula, governor of Walachia, advised him not to attack the emperor of the Turks with so small an army, since he went out every day a hunting with more men than such a number:

and I heard the number of them;
expressed by some angel, and therefore John was certain of it, otherwise he could not have told them.