For example, in the U.S. state of Virginia, such crossings include the Hampton Roads Bridge–Tunnel and the Monitor–Merrimac Memorial Bridge–Tunnel, both of which cross the harbor at Hampton Roads, and the Chesapeake Bay Bridge–Tunnel, a 37 kilometers long structure (including approach highways) that crosses the mouth of the Chesapeake Bay with a combination of bridges and tunnels across two widely separated shipping channels, using four artificial islands built in the bay as portals.