Principal Gate is located in front of the Throne Palace and facing the Flag Tower. Ngo Mon is the main entrance to the Imperial City. Ngo Mon is a huge construction, U-shaped and consisting of two parts: below is a foundation made of brick, Thanh and Quang stone, above is a pavilion made of wood and roofed with tiles.
The longest and widest sides of this 5.2m high foundation are 50m and 27m respectively. Ascent to the top can be made by two open stone staircases on both sides. There are five entrances, the main one being Ngo Mon, paved with Thanh stone, and with red-lacquered doors reserved for the Emperor. The two side-entrances, the Left and Right Gates, were for civil and military mandarins and, inside the branches of the U, are two more gates used by soldiers, elephants, and horses on the royal procession. The upper part is the Ngu Phung Pavilion (Pavilion of Five Phoenixes) in the middle, flanked by two wing belvederes of two stories.
Ngo Mon was also the site where the Emperor received homage from his subjects and ceremonies took place such as: Ceremony of Proclamation of Doctor Lists (successful candidates in the national examination), Calendar Offering Dayï¿½ On the side of the road passing the Ngo Mon stand two stone steles inscribed with "Tilt Your Hats and Dismount" reminding passers-by to tilt their hats and get off horses when passing this sanctum.
Ngo Mon was damaged during the wars and underwent several restorations.