4. Built cities. Evidently for defense and protection against both Israel and Syria, and against the rising power of Assyria which, under Tiglath-pileser III (745-727), was at this time taking an active interest in the affairs of Western Asia.
Castles. That is, forts. Both Uzziah and Jotham displayed an unusual anxiety to fortify the country (see 26:9-15). The prophets of the time denounced the popular confidence that was being placed in fortifications and human might (Hosea 8:14; Isa. 2:15; 17:3, 4).