Question: Do we celebrate Purim on the date that victory was declared in the Jewish war against their Persian enemies? When did the war commence and what was the war’s duration?
Answer: The war was fought on the 13th of the Jewish month of Adar. This was the date that our enemies meant to slaughter us. Instead, the Jews got the upper hand and, in the vast majority of locations, won the battle in one day. Therefore, the 14th (i.e. the day after the battle), was a day of rest and celebration, and was subsequently established as Purim day for all generations. In the capital of the Persian-Medean empire, Shushan, the fighting was also done on the 14th, and the people there rested and celebrated on the 15th. Therefore, Purim in Shushan (as well as all walled cities from the time of Joshua’s conquest of the land of Israel, such as Jerusalem) is celebrated on the 15th of Adar.
All the Best, Rabbi Azriel and Schreiber