I did not know about this sketch when I wrote my article on Helm's Deep.
It is nice to see the Professor's rendering so close in harmony with my own conclusions. Notice the "free-standing" citadel of the Hornburg. I used a chasm, but Tolkien connected the Hornburg by a wall to the base of the Thrihyrne (obviously the three peaks in the distance above the Aglarond caves). And as the view is toward the Hornburg, from the Deeping-comb, the layout is with the Hornburg on the south, north-facing wall of the canyon. (Evidence that Tolkien meant "north-facing" in the narrative.)
By way of noting contradictory details: although the Hornburg is in the correct position, the Hornburg gate and ramp would be utterly impossible to see from the Deeping-wall. Tolkien doesn't mention two Deeping-walls: but if we go by this sketch, then Aragorn and Éomer could have reached the west postern from this shorter wall: and also the Hornburg gate is almost visible from there. You can see the postern path coming around the base of the Hornburg wall to the main gate ramp. But the gate is still out of position, and I think it should be swung around ninety degrees to the viewer's left. It appears from the detail in the Deeping-wall and the wall around the Hornburg that Tolkien was considering them to be made of wood. An earlier (tentative) version of the battle of Helm's Deep (published by Christopher Tolkien in "The History of Middle-earth") describes a simple wall of piled boulders, without a Hornburg citadel at all. I have to wonder if this sketch is an interim study of J. R. R. Tolkien's while he was mapping out the final details of the story.
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