What is Shushan Purim?
Purim is observed on Adar 14, aligning with the victory of Jews in unwalled cities on Adar 13 and their subsequent rest day.
Conversely, in Shushan, the capital of the Persian Empire, Jewish triumph over adversaries spanned Adar 13–14, leading to rest on the 15th (Esther 9:20–22). This historical backdrop designated Adar 15 as the day for Shushan Jews to celebrate.
The Sages later decreed Adar 15 as Purim for all cities enclosed by walls during Joshua's conquest of Israel, emphasizing Jerusalem's significance. Although Shushan was not walled during Joshua's era, an exception was made due to the miracle.
Presently, deliberation continues about whether outlying Jerusalem neighborhoods should mark Purim on the 14th or 15th of Adar. Certain towns, like Chevron, Sfas, and others, celebrate Purim on the 14th, with an additional megillah reading on the 15th.
In diaspora locales such as Baghdad and Damascus, the 14th and an extra megillah reading on the 15th are commemorated. The clear delineation of the status of cities walled from Joshua's time is ongoing, with only Jerusalem adhering exclusively to Shushan Purim.
Beyond Jerusalem, many Jews observe Shushan Purim by donning festive attire, partaking in a tish, and exchanging mishloach manos - a custom rather than a mandate.