First known reference is from the Medieval Latin proverb, "It is Greek; it cannot be read."

The source for the quote is usually attributed to William Shakespeare in the play "Julius Caesar" (Casca, in Act I, Scene 2): "Those that understood him smiled at one another and shook their heads; but for mine own part, it was Greek to me."

"It's all Greek to me" or "I don’t understand any of this" or "This makes no sense."

A reference to something which is unintelligible or incapable of being understood.