The city wall you see in Nanjing today was built in 1366 (Yuan to Zheng 26 years) and completed in 1393 (Ming Hongwu 26 years), 27 years in all. Building it used 1 ministry, 3 weis, 5 provinces, 28 prefectures, and 152 prefectures and counties. A total of 280,000 migrant workers made it using about 350 million urban bricks.