Ho Citadel

The citadel was erected in 1397, during the Ho Dynasty. The stone citadel was built in the shape of a square with a gate on each side. The south wall gate is similar to the South Gate of Thang Long Wall. All four walls are surrounded by deep channels, protecting the Imperial Palace inside. Upon completion of the wall, King Ho Quy Ly moved the capital from Thang Long to Tay Do. The citadel was eventually destroyed and abandoned. Over 6 centuries have passed since the wall was erected, and only ruins of the South Gate remain.

Nowadays, inside the citadel are remains of the foundations of the royal places and two carved stone dragons.  

Source TCDLVN