Commentaire sur Middot 2:4

All the wall that were there. Regarding all the buildings on the Temple Mount.

All the walls that were there [in the Temple] were high except the eastern wall, for the priest who burned the red heifer would stand on the top of the Mount of Olives and direct his gaze carefully see the opening of the Sanctuary at the time of the sprinkling of the blood. The red heifer was burned on the Mount of Olives, towards the east of the Temple Mount. The priest who burned it had to see the Sanctuary when he sprinkled the blood. This is how the rabbis interpret Numbers 19:4, “the priest shall take some of its blood with his finger and sprinkle it seven times toward the front of the Tent of Meeting.” Note that the priest would not have been able to see the Sanctuary through the Eastern gate because the floor of the Sanctuary was 22 amot higher than the floor of the Temple Mount, and the Eastern Gate was only 20 amot high. Thus the floor of the Sanctuary was higher than the gate, and therefore, the priest had to see over the wall. That is why they designed this wall to be shorter than the other walls.

They were very high. Since all of their doorways were [already] twenty cubits tall, without [measuring the wall that continued] above the doorways.

Except for the eastern wall. It was the lowest of the ?retaining walls? (lit. feet) of the Temple Mount.

For the priest who burned the heifer would stand on the Mount of Olives (Har Hammishha). It is the Mount of Olives (Har Hazzeitim) that faces Jerusalem from the east. The priest would face west and look beyond the top of the wall [of the Temple Mount] through the gates that are within it to the doorway of the Hall, as he sprinkled the blood. As it is written: "Sprinkle it toward the front of the tent of meeting". (Numbers 19:4) If the wall was [as] tall [as the other walls], even though the gates were in line with each other, [meaning] the Temple Mount gate was directly opposite the Womens' Courtyard gate, and the Womens' Courtyard gate was opposite the Great Courtyard gate, and the Great Courtyard gate was opposite the doorway of the Hall, he would [still] not be able to see the doorway of the Hall through [all of] the gates, since the Mountain's slope increased to a height by which the ground of the doorway of the Hall was twenty two cubits taller than the ground on the foot of the Temple Mount, so the threshold of the Hall was higher than the lintel of the gate of the Temple Mount by two cubits, since the the gate of the Temple Mount was only twenty cubits tall as it was taught above. This means that the priest who slaughtered the heifer would not be able to see the doorway of the Hall through the gate [of the Temple Mount, therefore the eastern wall was shorter in order to allow the priest to see the doorway of the Hall from the Mount of Olives].