Why did the Japanese army choose Songshan as one of the four strongholds in western Yunnan?

Songshan is located on the west bank of Nujiang River, among the mountains west of Huitong Bridge, between Tengchong and Longling. It is more than 20 kilometers away from Huitong Bridge in the east, more than 50 kilometers away from Longling in the west, with shade in the south, loess slope in the north and the main peak of Songshan Mountain in the middle. It is one of the four Japanese strongholds in western Yunnan. Songshan Mountain is surrounded by mountains, and the terrain is steep. The Yunnan-Myanmar Highway winds around the canyon and is called "Gibraltar in the East" by the Allies. Songshan stronghold itself is strong, and it is a corner with Longling and Tengchong.

More than 3,000 people from the 56th Japanese Division 1 13 Brigade were stationed in Songshan. These Japanese devils have occupied Songshan Mountain for more than two years, building fortifications and setting up bunkers all over the mountain. The bunker is divided into three layers, the upper layer is used for observation and shooting, the middle layer is used as a bedroom or shooting, and the lower layer is used as a bunker and a warehouse for storing ammunition. The Japanese army is also equipped with hydropower facilities, which has the potential of "one person guards it, and ten thousand people can't", and it is the most difficult stronghold for the Japanese army to break through in the Yunnan-Burma campaign. Without Songshan, the expeditionary force could not seize Longling, and the Yunnan-Myanmar highway could not be unblocked.