Charles Ellicott Commentary 2 Samuel 10:17

"And it was told David; and he gathered all Israel together, and passed over the Jordan, and came to Helam. And the Syrians set themselves in array against David, and fought with him." — 2 Samuel 10:17 (ASV)

He gathered ... and passed. —David, hearing of the great Syrian rally, now took the field in person. Joab may have been with him, but more probably was employed at the south in holding the Ammonites in check and preventing their forming a junction with their confederates.