1 Chronicles 11:8

And he built the city round about. — Literally, and he built (or rebuilt or fortified) the city all round, from the Millo even unto the (complete) round. The Millo was probably a tower or citadel, like the Arx Antonia of later times. According to the chronicler David started from that point, and brought his line of defences round to it again. Samuel has simply, “And David built around, from the Millo, and inward.” This seems to mean that he carried his buildings from the fortress towards the interior of the city. Both statements may, of course, be true.