The early death of Zhu Yuanzhang's heir led to a succession struggle on his death, one that ended with the victory of Zhu Di and the declaration of the new Yongle era. Since his harsh treatment of the Ming capital Yingtian (modern Nanjing) alienated many there, he established his fief as a new co-capital. The city of Beiping became Beijing (“Northern Capital”) or Shuntian  in 1403. The construction of the new imperial residence, the Forbidden City, took from 1406 to 1420; this period was also responsible for several other of the modern city's major attractions, such as the Temple of Heaven and Tian'anmen. On 28 October 1420, the city was officially designated the capital of the Ming dynasty in the same year that the Forbidden City was completed. Beijing became the empire's primary capital, and Yingtian, also called Nanjing (“Southern Capital”), became the co-capital. (A 1425 order by Zhu Di's son, the Hongxi Emperor, to return the primary capital to Nanjing was never carried out: he died, probably of a heart attack, the next month. He was buried, like almost every Ming emperor to follow him, in an elaborate necropolis to Beijing's north.)