Were people buried near the Eastern Gate in OT times, or did this start post-Islam?

Pastor Armstrong taught that the Old Testament foretells the Messiah's return to Jerusalem through the East Gate:

Zech. 14:1  Behold, a day is coming for the LORD when the spoil taken from you will be divided among you.
Zech. 14:2 For I will gather all the nations against Jerusalem to battle, and the city will be captured, the houses plundered, the women ravished and half of the city exiled, but the rest of the people will not be cut off from the city.
Zech. 14:3 Then the LORD will go forth and fight against those nations, as when He fights on a day of battle.
Zech. 14:4 In that day His feet will stand on the Mount of Olives, which is in front of Jerusalem on the east; and the Mount of Olives will be split in its middle from east to west by a very large valley, so that half of the mountain will move toward the north and the other half toward the south.
Zech. 14:5 You will flee by the valley of My mountains, for the valley of the mountains will reach to Azel; yes, you will flee just as you fled before the earthquake in the days of Uzziah king of Judah. Then the LORD, my God, will come, and all the holy ones with Him!
Zech. 14:6  In that day there will be no light; the luminaries will dwindle.
Zech. 14:7 For it will be a unique day which is known to the LORD, neither day nor night, but it will come about that at evening time there will be light.

Because the Messiah was due to arrive on the Mt. of Olives before entering the city, Jews began burying their dead in that area in the hope they would be the first to greet the Messiah at His coming. Therefore, burial on the Mount of Olives started some 3,000 years ago in the days of the First Temple, and continues to this day. The cemetery contains anywhere between 70,000 and 150,000 tombs from various periods, including the tombs of famous figures in Jewish history.