In the first month ... - i. e. in March or April of 474 B.C.
“Pur” is supposed to be an old Persian word etymologically connected with the Latin “pars”, and signifying “part” or “lot.” The practice of casting lots to obtain a lucky day still obtains in the East, and is probably extremely ancient. A lot seems to have been cast, or a throw of some kind made, for each day of the month and each month of the year. The day and month which obtained the best throws were then selected. Assyrian calendars note lucky and unlucky days as early as the eighth century B.C. Lots were in use both among the Oriental and the Classical nations from a remote antiquity.
“Adar,” the twelfth month, corresponds nearly to our March. It seems to have derived its name from “adar”, “splendor,” because of the brightness of the sun and the flowers at that time.