Where are the other three?

When he opened the second seal, I heard the second living creature say, 'Come!' And out came another horse, bright red. Its rider was permitted to take peace from the earth, so that people should slay one another, and he was given a great sword.
(Revelation 6:3-4 ESV)

Apocalypse now? Well, as soon as the horse can cross the road.

Quite interesting Dolomites photo and history lesson here.