The Euphrates Army is said to be a colossal army of demonic spirits that shall rise from the river of Euphrates by four fallen angels riding upon the Locusts of Abaddon.
Description[]
According to a passage in the book of Revelations, the riders are described as having breastplates the color of fire and of hyacinth and of brimstone. The heads of the horses are like the heads of lions that spew out fire, smoke, and brimstone out of their mouths. Their tails are also said to be like serpents, which whom bite the heretics and heathens, causing them to experience the ultimate pain of which they are reduced to begging for their release; a fate similar to the locusts of Abaddon.
Overview[]
The Euphrates Army are known to be the most savage and unstoppable army in all of history to the point where no human could ever hope to defeat them even with their own advanced weapons at their disposal. According to John Constantine, these spirits were cultivated from the Beast of the Sea and likens them as parasites that made their home in the Beast's fur. They fed upon the sin and evil that was being collected by the Beast through the Tree of the Knowledge of Good and Evil in Limbo; this is also might explain as to why the Locusts of Abaddon resemble lion heads.
When the "Second Woe" is sounded, a group of fallen angels are the first to rise from the river with the named fallen being Yomyael, Beleth and Sitri before summoning their legion of two hundred million alongside them with the intent and purpose to kill a third of mankind.
The army will only rise when the end of the world is nearing the human race, or when the first several plagues and destructive events are wrought upon the world. In this case they were summoned when Satan ordered the fallen angels to bring forth the Euphrates Army in a bid to crush humanity's resistance as they attempted to destroy the Four Towers of Babel across the world while overwhelming the main army who took the fight directly to Lucifer, Satan, and the Beast.