Knights bound in the great river Euphrates, in a York Minster stained glass window

A larger image of Knights bound in the great river Euphrates, in a York Minster stained glass window

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Picture Source: Rick Steves Europe
The Great East Window, which is the size of a tennis court, is the single largest expanse of medieval stained glass in the country. It was created between 1405 and 1408 by master glazier John Thornton and shows the start and end of all things, from the world as described in the book of Genesis, to the events that will presage the end of the world and the second coming of Christ as told in the visionary Book of Revelation, know in the Middle Ages as the Apocalypse.
York Minster - Medieval stained glass

The Sixth Trumpet
13 And the sixth angel sounded the trumpet: and I heard a voice from the four horns of the great altar, which is before the eyes of God, 14Saying to the sixth angel, who had the trumpet: Loose the four angels, who are bound in the great river Euphrates. 15And the four angels were loosed, who were prepared for an hour, and a day, and a month, and a year: for to kill the third part of men. 16And the number of the army of horsemen was twenty thousand times ten thousand. And I heard the number of them. 17And thus I saw the horses in the vision: and they that sat on them, had breastplates of fire and of hyacinth and of brimstone, and the heads of the horses were as the heads of lions: and from their mouths proceeded fire, and smoke, and brimstone. 18And by these three plagues was slain the third part of men, by the fire and by the smoke and by the brimstone, which issued out of their mouths. 19For the power of the horses is in their mouths, and in their tails. For, their tails are like to serpents, and have heads: and with them they hurt. (Revelation 9:13-19 Douay-Rheims Bible)

See also Knights on Lion-Headed Horses in a York Minster stained glass window
Other 15th Century Illustrations of Costume & Soldiers