John Gill's  Exposition of the Bible 

2 Samuel 18:26

And the watchman saw another man running: and the watchman called unto the porter, and said, Behold another man running alone. And the king said, He also bringeth tidings.

And the watchman saw another man running,.... At a further distance:

And the watchman called unto the porter; that kept the gate, under which the watchtower was:

and said, Behold, another man runneth alone; as the other, and has the same appearance of a messenger:

And the king said, He also bringeth tidings; it being usual then, as now, to dispatch one messenger after another, as fresh accounts coming in made it necessary.