The angel swung his sickle on the earth, gathered its grapes and threw them into the great winepress of God’s wrath. They were trampled in the winepress outside the city, and blood flowed out of the press, rising as high as the horses’ bridles for a distance of 1,600 stadia.
Revelation 14:19-20
The winepress of God’s wrath appears here in Revelation, although winepresses are mentioned elsewhere. Whether a direct connection is necessary, or whether it is simply a common image is debatable, but here, as with the marriage supper of the lamb, a great slaughter is depicted.
In the timeline developed here, the winepress would come after the persecution of Domitian (the beast of Revelation, see here) in 96AD. It would also come before the bowls of wrath, which are apparent in the crisis of the third century, or 250AD.
In the year 135AD, we have such an event that fits the details of this vision almost perfectly.
Eighty thousand Romans entered Betar and slaughtered the men, women, and children until blood flowed from the doorways and sewers. Horses sank up until their nostrils and the rivers of blood lifted up rocks weighing forty se’ah and flowed into the sea where its stain was noticeable for a distance of four mil.
Jewish Talmud, Gittin 57
In the seige of Betar, which is located just outside the city of Jerusalem (Revelation 14:20), and some 500,000 Jews were slaughtered by the Romans in this the Second Jewish Revolt.
The Jewish Rabbinical account, above, depicts in language too similar to the Revelation account to ignore the slaughter and resulting bloodshed. There is a difference in distance in the two accounts, but that could either be that the Rabbinical account is wrong or that the 200 miles the Biblical account suggests, which is roughly the height of the entire nation, is either indicating that it is affecting the whole country, or perhaps some other measure is primarily indicated, such as circumference of the blood, a sum of all the streams in all directions, or some other accounting.
As for the blood reaching the nostrils of the horses, the language is such that this suggests not swimming in the blood in a canal as such, but that the blood was so deep, that a horse trodding through it would splash such a great quantity of blood that high as it was plodding through.