The Deeping Wall of Helms Deep was twenty feet high, and so thick that four men could walk side-by-side along the top.

It was sheltered by a parapet that few but the tallest of men could see over. In many places there were holes in the stone from where a man could shoot. On the inside you cold get to the top of the wall by a great stair, but on the outside there was no way up.
Encyclopedia entry originally written by Nienna-of-the-Valar