Bach embedded much musical and numerological symbolism into the Passion. For example, the key of E minor which opens the work has one sharp; in German the sharp was called a Kreuz, the same word for cross, making E minor the key of crucifixion. The libretto divided the events into two prologues and 15 "actions" but Bach further divides them into 27 actions. The number 27 was one of his favorite symbolic numbers, being a Trinitarian symbol (three to the third power).