Matthew Poole and continuators on 2 Samuel 18:24

24 And David sate between the two gates : and the watchman went up to the roof over the gate unto the wall , and lift up his eyes, and looked, and behold, a man running alone.

For the Gates of the Cities then were, as now they are, large and thick; and for the greater security, had two Gates, one more outward, the other inward. Here he sate, that he might hear tidings when any came into the City.

Unto the top of the Wall or Tower upon the Gate, where watchmen used to watch. Compare 2 King. 9. 17. Ezek. 33. 2.