Hanoi experienced a large number of earthquakes measured 6.0 on Richter scale and twice measured 7.0 on Richter scale in the 20th century. The phenomenon seems to increase considerably in Hanoi in recent years, causing a lot of faults in Northwestern and Southeastern regions, which have the same direction with Red River and see deep rifts on the earth’s crust.
Evidently, land in Hanoi is alluvial land raised by Red River’s silt; thus, the inner city is spotted by a wide range of lakes and lagoons, including West Lake (Ho Tay) and To Lich River. Hanoi was demonstrated as a city of fen and rivers, which was formed by half of land and half of water, according to an ancient map. The main territory of ancient Thang Long-Hanoi was alluvial land surrounded by Red River in the North and the East and by To Lich and Kim Nguu Rivers in the West and the South.
“The country’s center is shaped like a coiled dragon or a crouched tiger in the middle of the four directions and the terrain is sandwiched by mountains and rivers. The terrain there is wide and flat, high and bright; which will foster people’s living as well as development of all things. That location seems to be the best for the country’s capital aa well as the first-tier city of all kings,” former King Ly Cong Uan said in a royal letter to seek mandarins’ opinions about moving the royal citadel.
This can be regarded as the declaration of geopolitics and geo-strategies of Hanoi in the old days and the “belly-button” of Thang Long Royal Citadel is Nung Mountain, where kings of the Ly-Tran-Le Dynasties built Can Nguyen and Kinh Thien places and Nung Mountain. These places together with Cai River have become the two typical symbols of Nung Mountain-Nhi River royal citadel.