After losing the Yanyun Prefectures, the northern cavalry posed a constant threat. To prepare, scholars and pa…
After losing the Yanyun Prefectures, the northern cavalry posed a constant threat. To prepare, scholars and patriots devised an intricate tunnel system to connect every part of Qinghe.
But after the death of a wise ruler, the tunnels turned to ruins due to lack of repair. Eventually exploited by those with dark intentions.