What does Psalm 48:12 mean?

Perhaps the psalmist is addressing the travelers who reached Jerusalem and worshiped at the temple (Psalm 48:8–9). Or, this may be directed at the people of the city, poetically called "daughters of Judah" (Psalm 48:11). In either case, the writer points to the city's defensive structures which are intact (Psalm 48:13). Despite threats from massive armies (2 Kings 19) and the combined efforts of many nations (2 Chronicles 20), Jerusalem was intact thanks to the power of God (Psalm 48:1–7). Isaiah 33:18 seems to be a taunt, asking, "Where is he who counted the towers?" This refers to the scouts of Sennacherib, king of the army that failed to besiege the city.

In the ancient world, walls and other defensive measures were crucial parts of a city's existence. Years after the writing of this psalm, after Nehemiah led a post-exilic delegation back to Jerusalem, he and his workers finished rebuilding the city's walls. Then, he formed two processions with choirs and musicians to inspect the wall by walking around on top of it. After seeing that the wall was strong, everyone rejoiced and offered sacrifices (Nehemiah 12:31–43).