Revelation 9:13-19
The sixth angel sounded his trumpet, and I heard a voice coming from the horns of the golden altar that is before God.
It said to the sixth angel who had the trumpet, “Release the four angels who are bound at the great river Euphrates.”
And the four angels who had been kept ready for this very hour and day and month and year were released to kill a third of mankind.
The number of the mounted troops was two hundred million. I heard their number.
The horses and riders I saw in my vision looked like this: Their breastplates were fiery red, dark blue, and yellow as sulfur. The heads of the horses resembled the heads of lions, and out of their mouths came fire, smoke and sulfur.
A third of mankind was killed by the three plagues of fire, smoke and sulfur that came out of their mouths.
The power of the horses was in their mouths and in their tails; for their tails were like snakes, having heads with which they inflict injury.
Revelation 16:12
The sixth angel poured out his bowl on the great river Euphrates, and its water was dried up to prepare the way for the kings from the East.