Now the number of the troops of the equestrians: twenty thousand ten thousand [two hundred million]—I heard the number of them.
And so I saw the horses in the vision and the ones sitting upon them having fiery breastplates [bright red] also jacinth [deep blue], also sulfurous [vivid yellow], and the heads of the horses like heads of lions, and out of their mouths come fire and smoke and brimstone.
From of the three, this plague put to death the third of the people from the fire and the smoke and the brimstone coming out of their mouths.
For the horses’ empowerment is in their mouths and in their tails—for also their tails are similar to serpents, having heads, and in them they injure.
Revelation 9:16-19

Supernatural Steeds?
This is a continuation of the sixth trumpet, which unleashed the four angels held bound by the mighty Euphrates River. They are similar to the scorpionesque locusts, for these myriads of horsemen ride upon monstrous mounts with poisonous vipers for tails, and mouths that belch fire, brimstone, and noxious fumes. That is, in fact, the extraordinary power of these dreadful beasts.
What are we to make of them?
Two Hundred Million Horsemen?
It is worth noting that the estimated population of the entire earth in the first century lies somewhere between 150 to 330 million. In the ninth century it was 250 million, and it took seven centuries for that number to grow to 500 million by the sixteenth century. To have an army of literally 200 million equestrians even by the 1500’s would have been physically impossible.
Today, there is an estimated 7.9 billion people on the planet. However, there are still only about 7.25 million horses, which would be a little over 193 million shy of the number John saw.
So, how are we to deal with those numbers?
Historicist
Historicist scholars are quick to cite “two myriad of myriads” as an acceptable reading of John’s Greek, which would be a way of indicating a large, indefinite number. Correspondingly, both the Turkish and Tartar militaries counted their troops by myriads. The vivid red, yellow, and blue emblems were distinctive of the Ottoman Empire. Fire, brimstone, and smoke would be an eloquent and surprisingly accurate depiction of artillery—both cannons, and guns fired from horseback.
But what of the horses’ serpentine tails?
Evidently, during an early Turkoman battle, their army’s standards were all lost. A general seeking a quick and dramatic manner in which to rally his soldiers, cut off three (presumably already fallen) horses’ tails and affixed them to a spear. Brandishing this makeshift pennant, the general was able to lead his cavalry to victory.
From then on, it became a custom to attach horses’ tails to spears to create the Turkish army’s standards.

Preterist
Expositors concentrating on the downfall of Jerusalem agree that even two hundred thousand equestrians is an unrealistic depiction of the Roman army. However, if the meaning is to convey an overwhelming army, then that would accurately describe Rome’s concentration of armed forces in the siege of Jerusalem and subjugation of Judea.
Drastic Decree
God had warned the Israelites of what would come to pass should they transgress their solemn covenant with the Lord. A series of increasingly dire curses would advance upon them until finally, if they persisted in their unrepentance,
The Lord will bring a nation from far away, from the end of the earth, to swoop down on you like an eagle, a nation whose language you do not understand, a grim-faced nation showing no respect to the old or favor to the young….
It shall besiege you in all your towns until your high and fortified walls, in which you trusted, come down throughout your land; it shall besiege you in all your towns throughout the land that the Lord your God has given you.
God to the Israelites, Deuteronomy 28:49-50, 52 (NRSV)
In this final summary of God’s warning against transgression, not only would the people be besieged by a powerful army, but the famine would be so severe, parents would eat their children, pestilence would bring down many more, and in the end, what remnant remained would be scattered in exile. All these things occurred at least twice in recorded history. The first time in the exiles that happened before the second temple period, and the second time in the events surrounding and launched by the destruction of Jerusalem.
Two views prevail among preterists as the timing of this trumpet.
66 or 70 CE?
The first view maintains this invasion took place in 70 CE, when Jerusalem was breached, as this would close the trumpets section of John’s Apocalypse, and open the bowls of wrath, which have to do with God’s judgment on Rome.
The second view holds that all of John’s visions have to do with God’s judgment of Judea alone. In this case, the myriad horde represent the initial invasion of Judea in 66 CE, which brought General Cestius’s forces to the gates of God’s holy city in the month of Tishri. Roman troops surrounded the city just as the Day of Trumpets drew near.

Futurist
Commentators looking for a still future fulfillment remain undecided as to whether this is a demonic cavalry, or an uncountably huge human army.
Dark Spiritual Forces
If these are fallen angels now given over to the work of evil, then fire, brimstone, and smoke are all elements of hell brought to earth for nefarious purposes. Perhaps this is a continuation of the first demonic pack from perfidy, the ghastly locusts.
Human Horde
If these are actual soldiers, whether mounted horsemen or otherwise, the sheer numbers create a difficulty. For comparison,
- China—has an army of two million active soldiers.
- India—has nearly 1.5 million troops.
- United States—is not far behind with nearly 1.4 million in all of its armed forces.
- North Korea—currently counts 1.2 million at its military command.
Even if, for example, an eastern bloc were to be imagined, it would need an alarming and expeditious increase in recruitment to the tune of 196 hundred million draftees.
Nevertheless, considering the population of today, such an armed militia is technically possible to muster up.
Modern Warfare
Interpreters liken the vivid primary colors, as well as the fire, brimstone and smoke, to the conventional standards and equipment of current-day battle, depicted in the baroque language of John’s time. In particular, one expositor sees the explosion of nuclear weapons, likening the brimstone to molten shrapnel of buildings and earth, and the smoke as toxic radioactive fallout and debris, the worst of the killing agents.
The “two myriad of myriads” is understood as an irresistible, unstoppable, overwhelming military force teeming from the east to the west, that will decimate all Israel and Europe, and perhaps more, as a full third of humankind will be wiped out.

Spiritual
Perhaps the fifth and sixth trumpets, being so similar, are actually related, theorize the more spiritual theologians.
In that the former describes the internal corruption of a wicked culture, whereas the latter tells of external forces that bring down such a decayed society.
Steve Gregg, Revelation: Four Views A Parallel Commentary, p191
John may have been envisioning the fulfillment of a legendary fear of his century, that a Parthian host would one day gallop across the Euphrates and demolish the Roman Empire. Rome had never been able to conquer the powerful Arsacid Empire, centered in ancient Iran. In a sense, this could represent the besetting sins and spiritual afflictions people of every age fail to conquer.
Such spiritual ills are indeed myriad, threatening to overwhelm. They have the capability of destroying a third, which is to say a part but not the whole. Their weapons rise out of hell itself, as fire, brimstone, and smoke become foretastes of eternal judgment. Perhaps also the smoke represents the unwholesome atmosphere of false beliefs, and false life philosophies.
Alternatively, the locusts may speak to overwhelming spiritual forces and the horsemen to physical armies rising up out of the rebelliousness of humankind. Horses are a recognized symbol of warfare in scripture, and their serpent tails may be the aftermath of the violent conflicts that have pounded down through history. Again and again, war has brought famine, destruction, and trauma in its wake.

The four perspectives taken from Revelation: Four Views A Parallel Commentary, edited by Steve Gregg