Euphrates River · It rises in the highlands of modern Turkey, flows through Syria and Iraq, and joins the Tigris in southern Iraq before emptying into the Persian Gulf; at about 2,800 km it is Western Asia's longest river.
One of the four rivers of Eden, called simply “the River” in Scripture; in Revelation four bound angels are released there and its water dries up to open the way for kings from the east.
Background
The Euphrates was one of the four rivers flowing out of Eden and is often called simply “the River”; it formed the northeastern boundary of the Promised Land, “from the torrent valley of Egypt to the great river Euphrates.” Abraham's home city Ur and the whole Mesopotamian civilization lay in its basin, and it was the lifeblood of the Assyrian and Babylonian empires. It ringed and protected Babylon, until in 539 BCE Cyrus diverted its waters and marched in overnight, fulfilling the prophecies of Isaiah and Jeremiah. In Revelation the sixth trumpet releases the four angels “bound at the great river Euphrates,” bringing the plague of the cavalry, and when the sixth bowl is poured out its water dries up to prepare the way for kings from the rising of the sun. The river thus marks both the boundary God promised Abraham's offspring and the limit of human power.
Related Scriptures (New World Translation)
The name of the third river is Hidʹde·kel; it is the one going to the east of As·syrʹi·a. And the fourth river is the Eu·phraʹtes.— Genesis 2:14
The sixth angel blew his trumpet. And I heard one voice from the horns of the golden altar that is before God say to the sixth angel who had the trumpet: “Untie the four angels who are bound at the great river Eu·phraʹtes.”— Revelation 9:13-14
The sixth one poured out his bowl on the great river Eu·phraʹtes, and its water was dried up to prepare the way for the kings from the rising of the sun.— Revelation 16:12