Don’t forget to introduce: The total area of ​​various fortifications currently surveyed in the Hailar Fortress is more than 10,000 square meters, with more than 4,000 meters of underground passages, an area of ​​more than 5,000 square meters, and more than 50 rooms of various types, which can be guaranteed underground Basic daily life and combat supplies were called "underground cities" by Soviet war reporters. The deepest point of the underground fortification is 21 meters above the ground.