On the first of Adar [i.e., the last Hebrew month] they make proclamations regarding the shekel tax and kilayim [the prohibition of mixed vegetable gardens]. On the fifteenth [of Adar, i.e., Shushan Purim] they read the Megillah in [walled] cities and begin to repair the roads, plazas, and mikva’ot [ritual baths], and attend to all public works, and mark the graves, and send forth inspectors regarding kilayim.
The Torah (Exod. 30:12) commands the collection of a half-shekel poll tax from every male over twenty. While this may have been a one-time tax, later generations mandated its collection every year by the first of Nisan for the maintenance of the temple, and to pay for the daily sacrifices on behalf of the nation. One month prior to the due date, the government reminded people to pay the tax, and also adjured farmers to inspect their fields to remove forbidden mixtures that might have grown together over the winter. By Purim the raining season was over, and only a month remained until Pesah. Thus, it was important to clear the paths and plazas that would be used by pilgrims, and to help them be ritually pure by refilling ritual baths and refreshing the lime markers that indicated the presence of a grave. Stepping over a grave would render a person impure, and thus unable to enter the temple or eat the paschal lamb.