It is believed that Nanjing was the largest city in the world from 1358 to 1425 with a population of 487,000 in 1400. Nanjing remained the capital of the Ming Empire until 1421, when the third emperor of the Ming dynasty, the Yongle Emperor, relocated the capital to Beijing.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): When did Nanjing cease to be the capital?
1421