The phrase “The Writing on the Wall” has biblical origins.

It comes from the Book of Daniel.

The king of Babylon, Belshazzar (immediately preceded by Nebuchadnezzar*) used some ancient Jewish artifacts in a ritual praising the gods of gold, silver, and other non-god like things.

During the ceremony, a disembodied hand appeared and wrote a cryptic message, which the Babylonians couldn’t read.

Daniel, a Jew, is summoned, and he tells the king that the writing portends the fall of his kingdom.  Later that night the king dies.

So, when you can’t read the writing on the wall, it means you can’t see that something bad is going to happen.

* I only included the reference to Nebuchadnezzar so I’d have an excuse to use the name Nebuchadnezzar in a post.  Because it’s one of the best names of all time.