According to Revelation 14:19-20:
"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."
Perhaps we can use some maths to work out how many people would need to die to produce that amount of blood? My initial thoughts were millions but the maths proves otherwise.
Assuming that 1600 stadia is the diameter of the circle of affected ground (we don't get any idea of length from the text).
Assuming a horses bridle is 4 feet from the ground.
4 feet = 1.22m
1,600 stadia = 300km = 300,000m
We can then calculate the volume of blood using the formula:
V = lPIr2
V = 86,271 cubic metres or 86,271 litres of blood
Average amount of blood in a human body = 5.6 litres
By dividing the two we can work out how many dead bodies would be needed to produce that amount of bloood:
86271/5.6 = 15,405 bodies.
This does not take account of the displacement of bodies in the blood which could reduce the amount of dead by 75% or more, or the possibility that half the blood might be retained in the body, which could double the number of dead required to produce that amount of blood.
Therefore we have a minimum number of dead of only 3,851 (fully drained with displacement of bodies in the blood) or a maximum of 30,810 (half drained of blodd with no bodies to displace the volume to a height of four feet).
Either way both are not impossible and its not millions.
(80,000 people were killed immediately by the nuclear bombing of Hiroshima so even 30,810 dead in one battle is not unprecedented.)