This included the building of the flint walls, drawbridges and gatehouses. Surrounded by a moat, it has three entrances with drawbridges fronted by brickwork ravelins. These fortifications featured drawbridges which were raised at twilight. The villa's fortress theme is carried through by a surrounding moat and three drawbridges. The drawbridges to the front and rear have been replaced by wooden footbridges. The causeway crosses four islands and has two drawbridges. The first bridges were drawbridges; permanent bridges were not installed before 1688. So the gates were fortified and equipped with drawbridges. This was a clumsy arrangement, and many turning bridges were replaced with more advanced drawbridges. During the ancient times, the island was connected to the portico by two wooden drawbridges. Impressive drawbridges cross the Umpqua River at Reedsport and the mouth of Coos Bay. Past this interchange, the Baltimore Beltway continues west and returns to the Curtis Creek drawbridges. Three drawbridges over deep pits protected the access to the inner ward. Just north of the platforms, a pair of two-track drawbridges cross the Charles River. This includes drawbridges where traffic on the Interstate can be stopped for vessels.