The Northern Border City was called Guancheng.
Built of bluestone, it was mottled and weathered, as though it had endured ten thousand years of wind and rain, much like the many passes Lin Su had seen before.
Do not assume its history was truly so ancient. It looked so timeworn because it endured the flames of war every day. Even a newly built wall, after several months of high-intensity baptism by war, would become weathered enough. Weathering had never been merely a concept of time; it was also a concept filled with stories.
Lin Su had never been to Guancheng, but he had heard its story once and told it once.
The story he had heard came from Mo Qing.
Guancheng had faced a demonfolk invasion. A general had traveled millions of miles to beg the Mo family to build an impregnable city. A top-tier elder of the Mo family had gone and built them a defensive formation. But due to a miscalculation, eighty-seven Cloud Crystals were missing, turning the formation into a flawed product. During one massive demonfolk assault, the city fell and its people perished. The human race suffered casualties in the millions. That Mo family elder had thereafter withdrawn into the Mo family to reflect on his mistakes for a full eighteen years...
That had been Mo Qing's father!
So after Lin Su solved the Circle-Square Problem, she had traveled thousands of miles to Haining in search of the answer. That bastard Lin had lured her along, turn after turn, until she was still stuck at Haining Academy and unable to leave.
The person who told this story had been Lin Su himself!
During that day's debate at Wenyuan Pavilion, Lin Su had cited this story to prove his Arithmetic Dao, thereby establishing an independent school in