What does 2 Kings 23:16 mean?

As Josiah turned, he saw the tombs on the hillside. He had the bones taken out of the tombs and burned on the altar, defiling it, just as God’s man had said would happen. 2 Kings 23:16 - Modern Text Bible

(Josiah fulfills a prophecy by desecrating the altar at Bethel with human bones, making it unusable for idol worship.)