2 Chronicles 33:14
Now after this he built a wall without the city of David, on the west side of Gihon, in the valley, even to the entering in at the fish gate, and compassed about Ophel, and raised it up a very great height, and put captains of war in all the fenced cities of Judah.
Manasseh was born in the fifteen years added to Hezekiah's life after Hezekiah prayed for longer life, became one of the wickedest kings Judah ever had, and reigned fifty-five years, one of the longest reigns. After he was taken prisoner by the Assyrians he humbled himself, learned to know God, repented, and in wonderful mercy was restored, accepted, and returned to his kingdom, and the building work in this verse belongs to that restored time. The account including the verse is part of the events leading up to the Babylonian captivity, which came because of the people's transgressions.
After his restoration he strengthened Jerusalem's defenses by building an outer wall from the west side of Gihon through the valley to the entering in at the Fish Gate, encompassing Ophel, and raising it up to a very great height. He put captains of war and military commanders in all the fenced and fortified cities of Judah. By these defenses and by removing foreign idols and altars from the Lord's temple and repairing the profanations he had made against the Lord's house, he worked to repair the damage he had done.
This outward reform was part of his effort to repair his earlier sin, but it had only partial success and lasting evil effects remained.