1 Chronicles 11:5-7

5The people of Jebus taunted David, saying, “You’ll never get in here!” But David captured the fortress of Zion, which is now called the City of David.

6David had said to his troops, “Whoever is first to attack the Jebusites will become the commander of my armies!” And Joab, the son of David’s sister Zeruiah, was first to attack, so he became the commander of David’s armies.

7David made the fortress his home, and that is why it is called the City of David.