Da wikipedia:

The shows title refers to the river Rubicon in northeastern Italy, more specifically to the famous idiom "crossing the Rubicon", which means to pass a point of no return, and refers to Julius Caesar's crossing of the river in 49 BC, which was considered an act of war, because crossing it with an army was forbidden by the Roman Senate (this connection is explained by Kale Ingram in a speech to Katherine Rhumer in episode #12 to help her understand why her husband killed himself). Executive producer, Henry Bromell comments in press releases about the historic event, "They were always afraid that the Roman army would someday take over, which is exactly what happened," and continues "And that's when the republic ended and the empire—which is a dictatorship—began."

Sono al settimo episodio, assai interessante.