Albert Barnes Commentary 2 Kings 16:10

"And king Ahaz went to Damascus to meet Tiglath-pileser king of Assyria, and saw the altar that was at Damascus; and king Ahaz sent to Urijah the priest the fashion of the altar, and the pattern of it, according to all the workmanship thereof." — 2 Kings 16:10 (ASV)

And saw an altar - Rather, this refers to “The altar,” that is, an Assyrian altar connected with the formal recognition of Assyrian deities that the Ninevite monarchs appear to have required from all the nations they brought into their empire.

The fashion of the altar - Assyrian altars were not very elaborate, but they were very different from the Jewish ones. They were comparatively small and not well-suited for “whole burnt-offerings.” One type was square, about half the height of a man, and ornamented around the top with a battlement-style border. Another had a triangular base and a circular top made of a single flat stone. A third was a type of narrow, portable stand, about the height of a man. This last was the kind that the kings took with them on their expeditions.