Imperial Chinese military site at Tuen Mun [????- ]

A description of the location 

The first fort of which there is written record was known as Tuen Mun Chan and was almost certainly located at a point I have marked on the map, about three miles north of the present location called Tuen Mun. It would be an advantage if all doubts could be settled by excavation on the site, which can be seen even from the ground (and more clearly still from the air) to have contained old earth-works and possibly buildings.  

Source: Hong Kong before the Chinese K. M. A Barnett RASHK Vol 4 (1964) p. 42 

The valley between Castle Peak (which was an island) and the rest of Hong Kong was supposedly a navigable channel at the time which has since silted up. The fort possibly had visible remains in the 1960s.

The fort was built in 958AD although the name Tuen Mun Chan suggests an earlier fortification on the site

Cannot find the location on a modern map though so perhaps no remains exist