Lee,
From the interview W/ George Bahto that appears in the Feature Interview section of this website:
"What more accurate way to describe a 'Redan' than Macdonald's own words? 'Take a narrow tableland, tilt it a little from right to left, dig a deep bunker on the front side, approach it diagonally, and you have a Redan.' Bear in mind when Macdonald says 'tilt,' he means it. At National, hole #4 falls over five feet from front to rear. Redans are usually around 190 yards (a formidable distance in the early days of golf) with numerous strategic options depending on wind direction and course conditions: Fly it to the green if you are able, lay-up and chip on hoping to make three, hit a running shot at the banked area fronting the green or even play left of the Redan bunker hoping for a better approach angle (not recommended!). Behind the green are usually deep sand pits to catch aggressive play. To identify the best renditions, I would have to agree with this site's 'Discussion Group.' National's 4th and Piping Rock's 3rd are the most outstanding they built. Macdonald stated: 'the strategy of the Redan cannot be improved on.' The Redan strategy is used by nearly all architects - even as the green complex on par-4 holes. Redan traces its origin to the 15th at North Berwick where Davie Strath first built the hole while revising and formalizing the course. Sir David Baird, a former British Guards officer and a member at North Berwick, remarked that the escarpment Strath used at the 15th hole reminded him of the fortification he had stormed in Crimea 20 years before - the hole was immediately christened the 'Redan'."