Jamieson, Fausset and Brown on 1 Chronicles 26:17-19

17-19. Eastward were six Levites--because the gate there was the most frequented. There were four at the north gate; four at the south, at the storehouse which was adjoining the south, and which had two entrance gates, one leading in a southwesterly direction to the city, and the other direct west, two porters each. At the Parbar towards the west, there were six men posted--four at the causeway or ascent (1Ch 26:16), and two at Parbar, amounting to twenty-four in all, who were kept daily on guard.