This ancient battle tunnel was built in the years uneler the reign of emperor Zhen Zong in norerthrn song dynasty 。 The battle tunnel is four meters deep into the ground and is constructed wish grey bricks laid one on top of anther 。On the sides of the route are water troughs and jars for storing wanter There are lamps in the walls and ventilations in the ceiling ，the battle tunnel has a very deep well。On the two sides There are rooms where soldiers could hide inside 。The rooms are about two meters wide in which sub—tunnels could be found。 This winding anciern battle tunnel extents in all directions of the anciert town and can lead to its four gate towers 。 Preliminary gauging has tested the leagth of the tunarl to be about 1500 meters of which 400 meters have already been found and renovated Durring the years when the song dynasty and the liao Empire in the north were at war the troops of the liao Empire could only focus on defending themselves and dared not send their troops down south to invade the song due to the existence of these ancient tunnels which were both good for military assault and defense 。 By the Miang dynasty， The ancient tunnel became a military strong hold for fighting against Mongolian invaders ， whose military fanctions was further enhanced 。 Cultural relic experts believe that the ancient battle tunnel of zhang fang to be the only one of its kind found in Bei jing。 which has very high cultural and military values and has been listed as a municipality protected historic site。 In the Ming dyrasty An official renovated this tunnel and extended it by about 2 miles because it was a shortcut to go to his ancestor’s grvae 。 However this section had mostly collapsed and will be renovated in the future as a phase---two reconstrnction project 。 The original town tower of zhang fang was also destroyed during japanese invasion The new one we see today was rebuilt later on according to the original one。