Their assistants lived in the villages outside the city, and every seven days a group of them would come into the city and take their turn at guard duty.
The four full-time guards were Levites, and they supervised the other guards and were responsible for the rooms in the temple and the supplies kept there.
The Levites and the people of Judah followed Jehoiada's orders. The guards going off duty were not allowed to go home, and so each commander had all his guards available--those going off duty as well as those coming on duty.