https://www.mdpi.com/2073-445X/14/5/1087

> The Medieval (10th to 13th century CE) Wall System (MWS) stretches approximately 4000 km across extensive regions in northern China and Mongolia, as well as shorter sections in Russia (Figure 1). It represents one of the most extensive yet enigmatic architectural features in East Asia. In recent years The Wall Project, funded by the European Research Council, as well as other projects, has extensively studied and published on different sections of this wall line. Such research demonstrated that this extensive system of earthen walls was built by different empires from c. the 10th to the 13th centuries CE [1,2,3,4,5,6]. Among the different sections of the MWS, the wall section located in the southern Mongolia’s Gobi Desert is the least explored and still poorly understood. This study focuses on a 321 km-long segment of this wall line, located in Ömnögovi province of Mongolia, that we refer to as the Gobi Wall (Figure 2).

In any case, the traditional routes for the northern silk roads passed south of these walls through the Hexi corridor, at least until the Mongol period when many of them rerouted through the Orkhon valley north of the Gobi. Separate from the silk roads, there was a lot of trade/conflict between the northern Chinese states and the various Mongolian polities like the Liao. Managing that was both economically and existentially necessary for the border states like the xixia.

Also, nomads usually moved to the tax collectors instead of the other way around. More practical that way.