The stronghold of Zion - Or castle 1-Chronicles 11:5, 1-Chronicles 11:7. The ancient Zion was the hill on which the temple stood, and the castle seems to have been immediately to the north of the temple. The modern Zion lies to the southwest of the temple.
The same is the city of David - The name afterward given to it 2-Samuel 5:9, and by which it was known in the writer's time.

Nevertheless, David took the strong hold of Zion,.... A fortress without the city, and separate from it, and which was very strong; and the taking it might facilitate the taking of the city, which yet as appears by what follows, was very difficult to do:
the same is the city of David; it was afterwards so called, where he built an house, and dwelt.

the stronghold of Zion--Whether Zion be the southwestern hill commonly so-called, or the peak now level on the north of the temple mount, it is the towering height which catches the eye from every quarter--"the hill fort," "the rocky hold" of Jerusalem.