Ahaz is, however, a bad king, breaking Judah's record of good kings up to this point.
He even goes so far as to sacrifice his son in fire (probably to the god Moloch) and worships at various unsavory, polytheistic locations: trees and hills and so on.
But King Rezin of Aram and King Pekah of Israel attack Judah, while the Edomites take over the city of Elath, kicking out the Judeans.
Ahaz looks to King Tiglath-pileser of Assyria to bail him out. He offers him all the gold and silver and other treasures from the Temple and asks him to come and rescue Judah.
King Tiglath-pileser listens. He comes and captures Damascus from Israel, taking its people captive before finally killing King Rezin.
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When King Ahaz goes to visit and thank King Tiglath-pileser in Damascus, he is impressed by the altar he sees there. He decides to make some alterations to the altar and the Temple back in Jerusalem.
He sends an exact model and plans of the altar to the head priest, Uriah, who makes the required changes.
When Ahaz returns, he makes offerings at the altar, and gives Uriah further instructions for how to go about making these offerings. He also takes the bronze altar that was originally dedicated to God and uses it as a secondary altar next to the new one. The new one will be for his own personal inquiries to the gods or to God (it's not clear which).
He makes other alterations: he puts the molten sea on a stone pediment instead of on its bronze oxen pedestal, removes the frames of the Temple's stands, and also closes up one of the Temple's portals and one of its outer entrances.