As Prince of Yan (
燕王) he guarded the northern frontier from
北平, today's Beijing. When his nephew the
建文帝 began stripping the princes of their power, he rose in revolt in 1399, calling it
靖难 'quelling the troubles', and took
南京 in 1402. As the Yongle Emperor he built the
紫禁城, sent
郑和's fleets across the Indian Ocean and had the vast 《
永乐大典》 compiled.