Jerusalem: The Citadel of Mount Zion, Occupied by David, and Called the City of David
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2 Samuel 5:5–9
In Hebron he reigned over Judah seven years and six months, and in Jerusalem he reigned thirty-three years over all Israel and Judah. / Now the king and his men marched to Jerusalem against the Jebusites who inhabited the land. The Jebusites said to David: “You will never get in here. Even the blind and lame can repel you.” For they thought, “David cannot get in here.” / Nevertheless, David captured the fortress of Zion (that is, the City of David).
1 Chronicles 11:7
So David took up residence in the fortress; that is why it was called the City of David.