Charles Ellicott Commentary 2 Samuel 18:23

"But come what may, [said he], I will run. And he said unto him, Run. Then Ahimaaz ran by the way of the Plain, and outran the Cushite." — 2 Samuel 18:23 (ASV)

By the way of the plain. —The word used here is generally applied to the valley of the Jordan, and for this reason, it has been argued that the battle could not have been fought on the eastern side of the river, because if so, Ahimaaz could not have reached Mahanaim by the Jordan valley except by a long and tedious detour. But the word simply means circuit, or surrounding country, and is used in Nehemiah 12:28 for the country around Jerusalem. Here it means that Ahimaaz ran “by the way of the circuit,” i.e., in all probability, by a longer but smoother road than that taken by the Cushite, so that he was able to outrun him.