Esther 1:3 (ESV)

3 in the third year of his reign he gave a feast for all his officials and servants. The army of Persia and Media and the nobles and governors of the provinces were before him,

We know from historical accounts that in 484 BC, Ahasuerus had a decisive victory over his opponents in Egypt and Babylonia. Perhaps it was in order to celebrate this victory that he hosted a great banquet (feast) in the third year of his reign (that is, 483 BC).

At this banquet, the political and military leaders of all 127 provinces were present. This suggests that the number of guests amounted to thousands! The phrase Persia and Media refers to the whole empire. Media used to be the most powerful kingdom, before Cyrus I led Persia to domination (see Daniel 8:3, Daniel 8:20).