The Four Sponges of the Apocalypse are a holy prophecy who appear at the end of the Bible. They each represent War, Pestilence, Famine, and Death. They only appear briefly at the very end of the Bible, where their shadows are seen marching over the horizon to Jerusalem as pictured.
The Four Sponges of Apocalypse are destined to come at the end of time. See here for more details.