During the Ming dynasty, Nanjing was in its prime. Now we can find the most impressive remains of the Ming city wall of that dynasty. The wall is 33 km, the longest city wall in the world. And it took over 200,000 people build it during 1366 - 1386. Bricks from five provinces were used and each brick has been stamped with the origin, the overseer's name and rank, the bricklayer's name, and sometimes the date.