1,398. When to Read the Megillah

Hilchos Megillah v’Chanukah 1:4

The Sages established many different times for the megillah to be read, as seen from Esther 9:31, “to confirm these days of Purim in their appointed times.” The megillah is read as follows: If a city, either in or out of Israel, was surrounded by a wall at the time of Joshua, then they read the megillah on 15 Adar, even if the city is no longer surrounded by a wall. Such a city is referred to (in halachic discussions on this topic) as a “krach.” If a city was not surrounded by a wall at the time of Joshua, then the megillah is read on 14 Adar, even if the city is now surrounded by a wall. Such a city is referred to as an “ir.”

Hilchos Megillah v’Chanukah 1:5

In the Persian capital city of Shushan, the megillah is read on 15 Adar even though it was not surrounded by a wall at the time of Joshua. This is because the miracle occurred in that city and Jews at the time celebrated then as per Esther 9:18, “They rested on the fifteenth.” The rule about walls was based on the time of Joshua (even though the Purim story occurred much later) in order to honor the cities of Israel, which were in ruins at the time of the Purim miracle. Even though they are still in ruins, this would enable the residents of these cities to read the megillah on 15 Adar just like the residents of Shushan, since they were surrounded by a wall at the time of Joshua. In this way, the celebration of the miracle includes a commemoration of Israel.