The Nanjing City Wall is not just a geographic landmark; it represents the absolute zenith of human fortification history. As the longest surviving ancient city wall, its 35.3-kilometer perimeter far exceeds that of any contemporary European castle, effectively remaining an unconquerable masterpiece until the end of the cold weapon era. Interestingly, Emperor Zhu Yuanzhang utilized a strategy of "adapting to the mountains and rivers," resulting in a wall nearly 1.5 times the length of the Ming-era Beijing city wall. Furthermore, the project employed craftsmen from dozens of prefectures nationwide; each brick bears the names of its kiln, artisan, and even the supervising official. This early form of "accountability tracking" remains a marvel of engineering management, solidifying its undisputed top ranking.