'Fortress' in the Bible

and he leadeth them before the king of Moab, and they dwell with him all the days of David's being in the fortress.

And Gad the prophet saith unto David, 'Thou dost not abide in a fortress, go, and thou hast entered for thee the land of Judah;' and David goeth and entereth the forest of Hareth.

And David sweareth to Saul, and Saul goeth unto his house, and David and his men have gone up unto the fortress.