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View looking north at the special line of ancient stones at the foot of the northwestern stair case (on the right side of the photo) that leads up to the Temple Mount Platform. Leen Ritmeyer has argued that this line forms the western edge of the 500 x 500 cubit platform, described in the Mishnah, on which the Second Temple stood—and maybe the First Temple as well.
Modern stones may cover up some of the traces of older stones as well.
The structure at the far end of the line of stones is where the northwest "corner" of the ancient platform would have stood.