Jamieson, Fausset and Brown on 1 Kings 4:7

7. Solomon had twelve officers over all Israel--The royal revenues were raised according to the ancient, and still, in many parts, existing usage of the East, not in money payments, but in the produce of the soil. There would be always a considerable difficulty in the collection and transmission of these tithes (1Sa 8:15). Therefore, to facilitate the work, Solomon appointed twelve officers, who had each the charge of a tribe or particular district of country, from which, in monthly rotation, the supplies for the maintenance of the king's household were drawn, having first been deposited in "the store cities" which were erected for their reception (1Ki 9:19; 2Ch 8:4, 6).