Revelation 16:12
And the sixth [angel] poured out his bowl on the great Euphrates River and its water was dried up, so that the road would be prepared for the kings from the east [to travel on].
Revelation 9:14
It said to the sixth angel with the trumpet, "Release the four angels who are tied up at the great Euphrates River."
Revelation 7:2
And I saw another angel coming up from the east; he held the seal of the living God. [Note: This "seal" was a mark of identification or ownership]. And he called out with a loud voice to the four angels who had been given [the power] to harm the land and the ocean,
Revelation 11:14
The second Calamity is over; look, the third one is coming soon.
Revelation 17:15
Then the angel [See verses 1,7] said to me, "The waters you saw, on which the prostitute sits [See verse 1] are races, crowds, nations and language groups.