He built up the city around it, from the supporting terraces to the surrounding wall, while Joab restored the rest of the city.
Cross References
1 Chronicles 11:7So David took up residence in the fortress; that is why it was called the City of David.
1 Chronicles 11:9And David became greater and greater, for the LORD of Hosts was with him.
Treasury of Scripture
And he built the city round about, even from Millo round about: and Joab repaired the rest of the city.
Millo
Judges 9:6,20
And all the men of Shechem gathered together, and all the house of Millo, and went, and made Abimelech king, by the plain of the pillar that was in Shechem…
1 Kings 9:15
And this is the reason of the levy which king Solomon raised; for to build the house of the LORD, and his own house, and Millo, and the wall of Jerusalem, and Hazor, and Megiddo, and Gezer.
1 Kings 11:27
And this was the cause that he lifted up his hand against the king: Solomon built Millo, and repaired the breaches of the city of David his father.
repaired [heb] revived
Nehemiah 4:2
And he spake before his brethren and the army of Samaria, and said, What do these feeble Jews? will they fortify themselves? will they sacrifice? will they make an end in a day? will they revive the stones out of the heaps of the rubbish which are burned?