Today, Jews across the world are celebrating Purim — with one very notable exception: Jerusalem. In that most Jewish of cities, Purim will only be celebrated tomorrow, on the 15th of Adar. Why is that?
Among all the Jewish holidays, Purim has the singular distinction of having its date determined by whether or not a person lives in a city that was surrounded by a wall in the days of Joshua (ca. 1250 BCE).
“But the Jews in Shushan mustered on both the 13th and 14th days and so rested on the 15th and made it a day of feasting and merrymaking. That is why village Jews who live in unwalled towns observe the 14th day of the month Adar and make it a day merrymaking and feasting and as a holiday and an occasion for sending gifts to one another.” (Esther 9:18-9)
The sages considered making Shushan Purim — as the 15th of Adar is known, and which falls today, March 2 — conditional on whether a city was walled from the time of Ahasuerus, the Persian ruler of the time. But they did not wish to honor a Persian city over one in the Land of Israel, given that Israel was in ruins at the time of the Purim miracle. Joshua was chosen because, in the Book of Exodus, he is the general who begins the effort to annihilate the descendants of Haman’s ancestor, Amalek.
There are no cities in the Diaspora that were known to be walled 3,000 years ago, but for anyone visiting Jerusalem, be prepared to celebrate a joyous Shushan Purim.
As for Jericho, there is no Jewish community there today, although Shalom Al Yisrael, a Byzantine-era synagogue, was discovered there in 1936.
— Adapted from My Jewish Learning