Rev 9:
14 Saying to the sixth angel which had the trumpet, Loose the four angels which are bound in the great river Euphrates.

In the Greek Text, the four angels were not bound "in" the Euphrates but rather "on" or "upon" Euphrates. In the Strong Concordance, "Epi" means on or upon.

Be aware that the Sixth and Seventh Trumpets are directly linked to Daniel's Visions.

In Daniel, the Angel's words are like the voice of a multitude. According to the Apostle John, his voice was as the sound of many waters, in Revelation 17:15 it is explained that the waters are peoples, and multitudes..

Rev 1:
... one like unto the Son of man, clothed with a garment down to the foot, and girt about the paps with a GOLDEN GIRDLE.
14: His head and his hairs were white like wool, as white as snow; and HIS EYES WERE AS A FLAME OF FIRE;
15: And HIS FEET LIKE UNTO FINE BRASS, as if they burned in a furnace; and HIS VOICE AS THE SOUND OF MANY WATERS.
16: And he had in his right hand seven stars: and out of his mouth went a sharp twoedged sword: and HIS COUNTENANCE WAS AS THE SUN SHINETH IN HIS STRENGTH.

Dan:10:5:
... behold a certain man clothed in linen, whose loins were GIRDED WITH FINE GOLD of Uphaz:
6: His body also was like the beryl, and HIS FACE AS THE APPEARANCE OF LIGHTNING, and HIS EYES AS LAMPS OF FIRE, and his arms and HIS FEET LIKE IN COLOUR TO POLISHED BRASS, and the voice of HIS WORDS LIKE THE VOICE OF A MULTITUDE.

Also after the Sixth Trumpet sounded, in Revelation 10 John saw a mighty angel, his face was as it were the sun, and his feet as pillars of fire; lifting up his hand to heaven he swore by God, amazingly Daniel also had the same vision:

Rev 10:
5: And the angel which I saw stand upon the sea and upon the earth LIFTED UP HIS HAND TO HEAVEN,
6: AND SWARE BY HIM THAT LIVETH FOR EVER AND EVER, who created heaven, and the things that therein are, and the earth, and the things that therein are, and the sea, and the things which
are therein, that THERE SHOULD BE TIME NO LONGER:
7: But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished,

Daniel 12:6: And one said to the man clothed in linen, which was upon the waters of the river, How long shall it be to the end of these wonders?
7: And I heard the man clothed in linen, which was upon the waters of the river, WHEN HE HELD UP HIS RIGHT HAND AND HIS LEFT HAND UNTO HEAVEN, AND SWARE BY HIM THAT LIVETH FOR EVER that IT SHALL BE FOR A TIME, TIMES, AND AN HALF; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.

In Revelation the four Angels were bound on the Euphrates, yet according to the Translations of the Hebrew Text, Daniel had his vision by the Hiddekel.

Daniel was told to shut up the words, and seal the book. On the other hand, it is obvious that God had gifted Daniel with amazing Intelligence, so it is inconceivable that Daniel would call Hiddekel "the great River", knowing Euphrates means the great River. This was no Secret for Daniel and apparently he still used the term great River for another River. The only plausible and logical explanation is: we are dealing here with a Riddle.

Lookup the meaning of Hiddekel:
https://www.abarim-publications.com/Dictionary/ht/ht-d-he.html#.XyL0AL0pBvs

It means. sharp, keen and swift, (like the sword of the Spirit) in relation to the sharpness and keenness of the mind to resolve a riddle and be joyful.

When reading the text of Daniel's Vision, it may appear difficult to accurately establish the number of Angels, based on Revelation 9:14 we have the confirmation. four Angels were bound on the Euphrates,

Daniel 12:5
Then I Daniel looked, and, behold, there stood OTHER TWO, the one on this side of the bank of the river, and the other on that side of the bank of the river.

In plain English here is what one of the four Angels asked the Archangel upon the Euphrates: we are appointed to do the job, for how long to perform this "wondrous" work, when should we stop? (job description: kill by famine, pestilence, the sword and by this wild beast, the Roman Empire)

The Archangel swore by God, for a full 3 1/2 Years (1,260 Days) it shall be done until complete extermination of the wicked. The four Angels were bound by the Oath of the Archangel upon the great River, Euphrates.

Curiously when we add up the numbers of Revelation 9:15, 1 hour, 24 hours, 30 Days and 12 Months, we get 67. (1+24+30+12 = 67) In 67 AD, legions of Roman Soldiers that were based on the Euphrates met with General Vespasian and Titus, to form an army of 60,000 Men. After 3 1/2 years of war
, the Temple was destroyed and 30 days later Jerusalem fell.

Revelation 9
15 And the four angels were loosed, which were prepared for an hour, and a day, and a month, and a year, for to slay the third part of men.

Very Important Studies on Brighteon:
https://www.brighteon.com/channels/vpyt777