Emperor Taiwu of Northern Wei
The Northern Wei was engaged in protracted military conflict with the nomadic Rouran, who frequently raided the northern Chinese frontier to loot and pillage. Northern Wei emperors considered the Rouran to be uncivilized "barbarians" and called them "Ruanruan" or wriggling worms. According to the "Book of Wei", the dynasty's official history, Emperor Taiwu of Northern Wei launched a military expedition in 429 against the Rouran by advancing on the Black Mountain and then extending northward to the Yanran Mountain. Both locations are cited in "The Ballad". The Black Mountain corresponds to Shahu Mountain (殺虎山), located southeast of modern-day Hohhot in Inner Mongolia. Yan Mountain, the shorthand for Yanran Mountain (燕然山), is now known as the Khangai Mountains of central Mongolia. The Northern Wei sought to protect the frontier by establishing a string of frontier garrison commands across what is today Inner Mongolia.