In the present day east wall of the Har Habayis, around 200 feet to the north of the dome of the rock, is a sealed up double gate, called Sha'ar Harachamim-The Gate of Mercy. Through this gate, Moshiach is going to enter Yerushalayim. The Arabs put a cemetery right in front of it, and people say they did that so Eliyahu Hanavi, who is a Kohen, can't enter, because then he will become Tamei. (The Arabs didn't know that a kohen is allowed to walk over a non-Jewish grave, as long as he doesn't touch it. [Rambam, Hilchos Tumas Meis, a1:13) 
   But who made this gate? when? and why?

    The Mishnah (Middos 2:1) says that the Har Habayis had the majority of the empty space in the south, the second biggest in the east, third in the north, and the least in the south. most Meforshim explain that this means the empty space between the Azarah walls and the walls of Har Habayis, and this is how I made my calculations of where the original Har Habayis was. However, there is another opinion, (R' Yehosef Ashkenazi, brought by the Meleches Shlomo, this opinion is also brought by Maharam Kazis) that it means the space between the Har Habayis walls and the walls of the Azarah and the Ezras Nashim.

In a previous post, I wrote that the Migrash of Har Habayis went until the western wall of the present day temple mount, the Kosel Hama'aravi. However, there is a problem with saying that, because the stones of the Kosel are all Herodian-style stones (stones with margins and smooth bosses), and there are no seams to mark the beginning of Hurdus's extension, so it can't be from the time of Shlomo Hamelech.
    
    In order to solve this problem, I will point out something strange about the Kosel. The southern wall of the present day Har Habayis is 2.25 meters (27.7 ft.) thick (The Quest, page 69). The eastern wall is 2.88 meters (9 ft. 6 in.) thick (Survey of Western Palestine-Jerusalem, page 238). The western wall, however, is almost double that, it is 4.60 meters (15 ft.) thick! (The Quest, pages 25, 29). 
     
   It seems that the reason for this is that originally the Kosel was built by Shlomo Hamelech. Hurdus, when he rebuilt the Beis Hamikdash, added another wall right in front of Shlomo's, hiding Shlomo's wall. For this reason, the Kosel is almost double as thick as the other walls, because it is really two walls. (A possible reason why Hurdus did this is because this wall was by one of the main streets of Yerushalayim, so he wanted it to look smooth.) For this reason, we daven by this part of the Kosel, and not opposite the Kodesh Hakodoshim, because right here the wall is partly from the first Beis Hamikdash.