Jamieson, Fausset and Brown on 2 Samuel 18:23

23. by the way of the plain--or ciccar, "circle." This word is only used elsewhere in connection with the valley of the Jordan. It is possible that there may have been a place or region so called on the tablelands of Gilead, as the Septuagint seems to indicate. Or Mahanaim may have been so situated, with the regard to the battlefield, as to be more easily accessible by a descent to the plain of the Jordan, than over the hills themselves. Or the word may signify (as Ewald explains) a manner of quick running [Stanley].