2 Samuel 5:7-9

Nevertheless, David captured the stronghold (fortress) of Zion, that is, the City of David. Then David said on that day, “Whoever strikes the Jebusites, let him go up through the [underground] water shaft to strike the lame and the blind, who are detested by David’s soul [because of their arrogance].” So [for that reason] they say, “The blind or the lame (Jebusites) shall not come into the [royal] house [of Israel].” [1 Chr 11:6] So David lived in the stronghold and called it the City of David. And he built all around [the surrounding area] from the Millo [fortification] and inward.