2 Samuel 5:6-9

Now the king and his men went to Jerusalem against the Jebusites, the inhabitants of the land, who said to David, “You shall not enter here, for the blind and the lame [even the weakest among us] will turn you away”; they thought, “David cannot come in here [because the walls are impenetrable].” 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.