The current practice is that Purim is celebrated as a one-day holiday. Cities that were walled at the time of Joshua’s conquest of Israel — most notably Jerusalem — celebrate Purim on Adar 15, as a commemoration of the end of hostilities in the walled city of Shushan, where the battles occurred on Adar 13 and 14. Elsewhere, the holiday is observed on the one day of Adar 14, to recall the cessation of the battle after the war on the thirteenth in all other places of Ahasuerus’s kingdom. The rabbis, not the book of Esther, determined that cities that had walls since the days of Joshua were obliged to observe Purim on Adar 15. In contrast to the practice of a one-day Purim holiday, the book of Esther states, as I will show, that the holiday should be observed by everyone on two days — on both the 14th and 15th of Adar.
It is possible that the date of the Purim holiday developed in three stages. It was first accepted as a holiday on the fourteenth only in the villages, as Esther 9:19 records: “As a result [of the successful defensive battle against the non-Judeans on Adar 13–14], Judeans of the villages, who dwell in villages, make the fourteenth of Adar a day of happiness, feasting, and a good day, and of sending portions one to another.”
Two things should be noted about verse 19, which details the first stage of the development of the Purim holiday. Firstly, the holiday was celebrated for one day, Adar 14, by villagers. Verse 18 states that the Judeans battled for two days — both the thirteenth and the fourteenth – “and rested on the 15th day and made it a day of feasting and happiness.” But as A. Cohen notes on verse 19, “After this verse we would have expected another verse giving the law of ‘Shushan Purim,’ that those who dwell in walled cities keep the 15th of Adar” as the holiday of Purim. Since this is absent, it seems that the first stage of the celebration of Purim was a single day, on Adar 14. Secondly, this celebration was accompanied by sending gifts to one another. No mention is made of gifts to the poor.
The second stage was developed later. Mordecai decreed that Purim should be observed for two days, as indicated in verses 20–22 and 27. Mordecai sent a letter to all Judeans of Ahasuerus’s provinces “to accept upon themselves to keep the 14th of the month of Adar and the 15th of it, every year…and make them days of feasting and happiness and of sending portions one to another and gifts to the poor.” And the Judeans “took upon themselves…that they would keep these two days.”
Again, two things should be noted: (1) Mordecai made Purim into a two-day holiday and requested the people to accept it as such, and they did. (2) He added the practice of sending gifts to the poor.
Josephus, writing after 70 CE, records that Purim was celebrated on Adar 14 and 15 – two days. He states that the people sent gifts to one another. He does not mention gifts to the poor.
Still later, for unknown reasons, the practice arose to observe only a single day of Purim. Cities like Jerusalem that were walled during the days of Joshua observed Purim on Adar 15, while all other cities observed it on Adar 14.
In sum, we see that the biblical holiday of Purim underwent changes, and it is practiced today differently than the Torah mandates.
 The Hebrew manot, “portions,” does not indicate what the portions were, but the Talmud states it is foodstuff, and since the plural is used, the rabbis decreed it should be at least two foods.
 The Five Megilloth (Soncino Press, 1952), 238. The Babylonian Talmud, Megilla 2b, also notes that the law for the walled cities is absent.
 It should be noted that Mordecai did not say send “portions,” but gifts. It is unclear whether portions and gifts should be understood as synonyms or as two different kinds of things.
 Antiquities 6:13.
 The issue is discussed in the Babylonian Talmud, Megilla 2b.