What was the administrative level of Yan 'an in ancient times?

The highest position of Yan 'an in ancient times was in the Northern Song Dynasty. Because of the war with Xixia, there was a special service in the Northern Song Dynasty in Wu Ruo. The Western Army is led by historical celebrities, such as Fan Zhongyan, Di Qing, Lao Zhong and Tong Guan. The marked army is divided into six military regions, and Yan 'an is one of the military bases, which is municipal, though weak.