He built the high gate of the house of the LORD, and on the wall of Ophel he built much. On the wall of Ophel - The wall, says the Targum, of the interior palace. Ophel was some part of the wall of Jerusalem, that was most pregnable, and therefore Jotham fortified it in a particular manner.
Related Commentaries of 2 Chronicles 27:3
2 Chronicles 27:3
3 He built the high gate of the house of the LORD, and on the wall of Ophela he built much.