The duration of the incident is naturally defined by its geography: the earlier the Japanese entered the area, the longer the duration. The Battle of Nanking ended on December 13, when the divisions of the Japanese Army entered the walled city of Nanjing. The Tokyo War Crime Tribunal defined the period of the massacre to the ensuing six weeks. More conservative estimates say that the massacre started on December 14, when the troops entered the Safety Zone, and that it lasted for six weeks. Historians who define the Nanjing Massacre as having started from the time that the Japanese Army entered Jiangsu province push the beginning of the massacre to around mid-November to early December (Suzhou fell on November 19), and extended the end of the massacre to late March 1938.