Cities: Designated as Royal

So Adoni-zedek and his people were greatly alarmed, because Gibeon was a great city, like one of the royal cities; it was larger than Ai, and all its men were mighty.

Then David said to Achish, “If I have found favor in your eyes, let me be assigned a place in one of the outlying towns, so I can live there. For why should your servant live in the royal city with you?”

Meanwhile, Joab fought against Rabbah of the Ammonites and captured the royal fortress.

So David took up residence in the fortress; that is why it was called the City of David.