Political elites use not only direct force but also ritual to bolster their authority. (1) The use of ritual is very old and includes examples such as the cult of the Roman emperor, which some now believe is what held the Roman Empire together in the absence of a "credible" military threat. (2) The celebration of holidays is one way that elites use ritual to construct political legitimacy for a dynasty or the nation-state. (3) Thus, Roman emperors had their accession days--dies imperii--that were celebrated annually. In England, accession days were not celebrated until about 1570, when the government of Queen Elizabeth I encouraged prayer and festivity on November 17, the anniversary of the queen's accession, in order to bind the nation to the ruling dynasty. (4) Republics have replaced accession days with days commemorating the founding of the government; thus, France exchanged dynastic celebrations for the annual holiday of July 14, or Bastille Day. (5) The Romans did not invent the celebration of accession days. There is evidence for the annual celebration of the accession day of at least one Achaemenid king--the Persian festival of Magophonia. This festival in fact celebrated the accession of Darius (522-486 B.C.E.), because it commemorated the victory of Darius over a competitor to the throne, marking the beginning of a new, although perhaps distantly related, dynasty. (6) In this essay, I argue that Purim originally celebrated the accession day of Mordecai the Jew.