In 19 B.C.E. the master-builder, King Herod the Great, began the most ambitious building project of his life, the rebuilding of the Temple in lavish style. To facilitate this, he undertook a further expansion of the Hasmonean Temple Mount by extending it on three sides, to the north, west and south.
The former extension required the filling in of a deep valley to the north of the pre-Herodian Temple Mount. The Shushan Gate remained the only gate in the Eastern Wall. Towers were erected at each corner and a large water reservoir was built at the northeast corner, the so-called Pool of Israel. At the northwest corner, the massive Antonia Fortress was built to protect the Temple against attacks coming from the north and to guard the mount in times of strife.