'Stronghold' in the Bible

Yet David did capture the stronghold of Zion, that is, the city of David.

David took up residence in the stronghold, which he named the city of David. He built it up all the way around from the supporting terraces inward.

When the Philistines heard that David had been anointed king over Israel, they all went in search of David, but he heard about it and went down to the stronghold.

my God, my mountain where I seek refuge.My shield, the horn of my salvation, my stronghold, my refuge,and my Savior, You save me from violence.

At that time David was in the stronghold, and a Philistine garrison was at Bethlehem.