So David dwelt in the fort
The strong hold of Zion, which he took:
and called it the city of David;
from his own name, to keep up the memory of his taking it, and of his habitation in it:
and David built round about, from Millo and inward;
built a wall about it, and enlarged the place, increased the buildings both within and without. Millo is supposed to be a ditch round the fort, full of water, from whence it had its name; or was a large hollow place which divided the fort from the lower city, and which afterwards Solomon filled up, and made it a level, and therefore is called so here by anticipation; though Jarchi says it was done by David. According to Dr. Lightfoot {o}, it was a part or Sion, or some hillock, east up against it on the west side; his first sense is best, Millo being no other than the fortress or citadel; which, as Josephus says F16, David joined to the lower city, and made them one body, and erecting walls about it made Joab superintendent of them; and this was the "round about", or circuit, which David made, reaching from Millo, or the citadel, to that again, which is meant by "inward", or "to the house" F17, as it should be rendered; that is, to the house of Millo, as in ( 2 Kings 12:20 ) ; and so it is said ( 1 Chronicles 11:8 ) ; that David built the city "from Millo round about"; that is, to the same place from whence he began F18.