The story goes that the Yongle Emperor killed 2800 concubines, serving-girls, eunuchs, and others in the Forbidden City in 1421, apparently to quash humiliating rumours by killing all the witnesses. But most accounts I've found are from tabloids and blogs, and I'm having trouble finding any real, reliable literature.

Did it happen? If it did, why and how? It seems overkill relative to the motive.