The Golden gate, located at the north section of the east wall of the Haram, with its delightful white-washed double-domes and double arches from both sides, is a source of many traditions. In Jewish belief the gate, that has been blocked for centuries, is called 'The Gate of Mercy' (shaar harakhamim), and is considered to be the place from which the Messiah will enter in the end of days, this is where one asks for mercy before the Day of Judgment. The gate, which some believe existed from Herodian times of the Jewish Temple is believed to be the place from which Christ entered Jerusalem on the Sunday preceding his crucifixion (Palm Sunday), and was thus implying his own messianic status. This place is where Virgin Mary's parents met after an angel had promised her birth, marking the gate as the symbol of Mary's immaculate conception. In Islamic tradition the gate is also the site where some of the events of the Day of Judgment will occur; the entrance of the Messiah to Jerusalem and the entering of the righteousness people through the north gate, the 'Gate of Grace', while the others will enter through the south gate, the 'Gate of Mercy'.
The original date of construction is much debated. There are evidences that the gate was built to replace an older gate. Some traditions associates the gate with Herodian times as being the beautiful gate mentioned in the New Testament that led from the forecourt of the heathens into the Women's forecourt. Many identify the gate as belong to Byzantine times of late 6th century or 7th century. Others suggest that it is the construction of Caliph al-Walid at the beginning of the 8th century.
Sources:
Burgoyne, Michael Hamilton. 1987. Mamluk Jerusalem: An Architectural Study. Jerusalem: British School of Archeology in Jerusalem, 273-298
Burgoyne, Michael Hamilton. 1992. The Gates of the Haram al-Sharif. In Bayt al-Maqdis: Abd al-Malik Jerusalem. edited by Raby, Julian and Johns, Jeremy. Oxford: Oxford University Press, 114
Mehling Franz N., Paukert Maria, Pollmann Bernhard and Studemund Michael. Jerusalem and the Holy Land. Edited by Mehling Marianne. Oxford: Phaidon, 169-170