Albert Barnes Commentary 2 Chronicles 27:3

"He built the upper gate of the house of Jehovah, and on the wall of Ophel he built much." — 2 Chronicles 27:3 (ASV)

Ophel was the name given to the long, narrowish, rounded spur or promontory that lies between the central valley of Jerusalem (the Tyropoeon) and the Kidron, or valley of Jehoshaphat. The anxiety of Uzziah and Jotham to fortify their territory indicates a fear of external attack, which at this time was probably felt mainly in connection with Samaria and Syria (2 Kings 15:37). This faithless trust placed in fortifications was rebuked by the prophets of the time (Hosea 8:14; Isaiah 2:15).