2 Kings 23:20
And he slew all the priests of the high places that were there upon the altars, and burned men’s bones upon them, and returned to Jerusalem. And he slew all the priests of the high places that were there upon the altars, and burned men’s bones upon them, and returned to Jerusalem.
After long years in which the people had followed surrounding nations in bowing to images of wood and stone, removing every trace of idolatry seemed almost beyond human power, yet Josiah persevered in cleansing the land. He met idolatry firmly and sternly, slaying all the priests of the high places upon their altars and burning men's bones upon them. In this he destroyed every remaining vestige of idol worship in Judah and Jerusalem in order to cleanse the land.
He did this to carry out and perform the words of the law written in the book found in the temple. That book had been found by Hilkiah the priest in the house of the Lord, and Josiah's action belonged to the reformation that followed the renewal of the covenant.