Crossing the Styx
If you “cross the Styx” you journey to the underworld. Just like Hercules, Theseus, Orpheus, Odysseus, Aeneas, and Dante did.
Crossing the Hellespont
If you “cross the Hellespont” you make a greedy, short-lived attempt at seizing power. Just like Xerxes when he crossed the Hellespont to invade Greece, and Alexander the Great when he crossed the Hellespont to invade Asia.
Crossing the Rubicon
If you “cross the Rubicon” you make a bold decision that can never be taken back. Just like Julius Caesar when he crossed the Rubicon and started the civil war that turned the Roman republic into an empire.
Crossing the Jordan
If you “cross the Jordan” you find salvation. Just like the Israelites who escaped slavery in Egypt by crossing the Jordan into the Promised Land, and the gospel singers who talk about crossing the Jordan into the afterlife.
Crossing the Delaware
If you “cross the Delaware” you take a surprising action that succeeds against improbable odds. Just like George Washington when he crossed the Delaware for a surprise attack on the Hessian mercenaries in Trenton.