דברי הימים א, פרק י״א, פסוק ח׳

Capturing Jerusalem and establishing it as the kingdom's capital sparked a massive wave of building and development. The effort to fortify the city, expand its central districts, and rebuild past ruins required a division of leadership between the king and his army commander.

The heart of this construction focused on a specific central area. Some explain this was an open square near the city wall used for public gatherings [מצודת דוד, רד״ק]. Others suggest it referred to empty spaces between the fortress and the wall, which earned their name because David and Solomon eventually filled them with new buildings [ביאור שטיינזלץ]. David directed the construction inward from this central point, either enclosing the entire district completely [מצודת דוד] or extending the building all the way to a surrounding watchtower [רד״ק]. Despite these major efforts, the city's defenses were not fully completed during David's reign. Parts of Jerusalem remained exposed until King Solomon later finished the wall and closed the remaining gaps [מלבי״ם, ביאור שטיינזלץ, רד״ק].

While David personally oversaw the development of his own residential district in the City of David, he placed his commander Joab in charge of managing the rest of Jerusalem. Joab's mission was to bring the remaining parts of the city back to life. The primary approach among commentators is that this revival was a physical reconstruction. Joab restored the ruined sections of the city, built new towers, and repaired the damaged walls, effectively healing the broken stones and structures. Alternatively, this revival was social and economic. In this view, Joab breathed new life into Jerusalem by bringing in new residents, transforming it into a bustling city, and ensuring the local people had steady livelihoods and a reliable food supply [מלבי״ם, ביאור שטיינזלץ].