2 Kings 12:20

And his servants arose
This was after he had slain Zechariah the son of Jehoiada, who reproved him for his idolatry; and after a second expedition of the king of Syria, who came to Jerusalem, and spoiled it, and left Jehoash diseased, as is recorded in ( 2 Chronicles 24:23-26 ) ,

and made a conspiracy;
not to get the kingdom into their hands, for his son succeeded him, but to avenge the death of Zechariah;

and slew Jehoash in the house of Millo, which goeth down to Silla;
these are both names of places; perhaps the latter is mentioned, to distinguish this Bethmillo from Millo in Zion; or rather that itself is meant, and described by the descent from it to a causeway, as Silla may signify, which led to the royal palace.