A moratorium is in effect on adding information from Fire and Blood until December 20th.
The King's Gate is one of the seven huge gates that surround the huge walls of King's Landing. It is by the southern corner of the southwest wall, connecting the western end of the River Row to the tourney grounds outside the city's wall by the Blackwater Rush. There is a sally port in it.
In the reign of Maegor I Targaryen, Maegor had his own wife and queen; Alys Harroway tortured to death and executed. Following her death, Alys body was cut into seven parts and mounted on spikes above each of the seven gates of the city, one of which was above the King's Gate.