Probably a fortified area in the northern part of the ancient Jebusite city captured by David. David had done much work to strengthen this area (2 Sam. 5:9; 1 Chron. 11:8), and the main fortification was completed by Solomon (1 Kings 11:27). Joash had probably been confined in this house of Millo chiefly for security reasons.
Slew Joash.
When the Syrians departed “they left him [Joash] in great diseases” (2 Chron. 24:25), evidently sorely wounded. While Joash was confined to his bed the conspirators slew him. The conspiracy was obviously connected with the king’s apostasy and the base murder of Zechariah, the son of Jehoiada. Joash owed his life and his throne to the faithful high priest. It was an act of base ingratitude to slay the son of his benefactor. So great was the sentiment against Joash that at his death “they buried him not in the sepulchres of the kings” (2 Chron. 24:25).