C. F. Keil and Franz Delitzsch on 2 Chronicles 27:3-4

2Ch 27:3-4

He built the upper gate of the house of Jahve, i.e., the northern gate of the inner or upper court (see on 2Ki 15:35); the only work of his reign which is mentioned in the book of Kings. But besides this, he continued the fortifying of Jerusalem, which his father had commenced; building much at the wall of the Ophel. העפל was the name of the southern slope of the temple mountain (see on 2Ch 33:14); the wall of Ophel is consequently the wall connecting Zion with the temple mountain, at which Uzziah had already built (see on 2Ch 26:9). He likewise carried on his father’s buildings for the protection of the herds (2Ch 26:10), building the cities in the mountains of Judah, and castles (בּירניּות,   2Ch 17:12) and towers in the forests of the mountains of Judah (חרשׁים from חרשׁ, a thicket).