"Based on the limit that one city can only cover two prefectures at most,
If I want to completely defend a county, one defense line would require at least five cities to be garrisoned. Only then can we ensure it won't be infiltrated by the Barbarians.
But in reality, all I actually need to do is ensure that among the four defense lines, the area close to the hinterland is secured, preventing the Barbarians from crossing that region and infiltrating the rear.
Among the four defense lines, those areas that are not adjacent to the rear can actually be somewhat abandoned.
Just like Xu State previously, in order to block my forces, only stationed troops in Dongping County's central and southern cities, Xichang and Shouzhang, which covered only half the county's area, was enough to stop my central military expedition from advancing further east.
