I have worked for 1-1/2 weeks clearing city fortifications that date to the time of the biblical King David. The city walls at Khirbet Qeiyafa are casemates and served as living space during peacetime.
The doorway in this short video was blocked up several centuries before Christ. It was opened up again on July 20, 2010.
The bottom of the casemate is not visible in the video above. The exposed bedrock is around 5-1/2 or 6 feet below the level on which I am standing.
Here is a photo taken before the entrance was opened. Notice the straight line that reveals the ancient doorway.