2 Kings 23:20

And he slew all the priests of the high places that were
there
The idolatrous priests who sacrificed to Baal, and other Heathen deities; for as for others that burnt incense in high places, yet to the true God, those he spared, though they were not suffered to officiate at the altar of God: the others he slew

upon the altars;
where they sacrificed:

and burnt men's bones upon them:
the bones of the priests, and worshippers of idols, as he had done at Bethel:

and returned to Jerusalem;
after he had gone through the land, both of Judah and Israel, and abolished idolatrous worship everywhere.