Charles Ellicott Commentary 2 Samuel 18:2

"And David sent forth the people, a third part under the hand of Joab, and a third part under the hand of Abishai the son of Zeruiah, Joab`s brother, and a third part under the hand of Ittai the Gittite. And the king said unto the people, I will surely go forth with you myself also." — 2 Samuel 18:2 (ASV)

Ittai the Gittite. —Compare note on Judges 15:19. The arrangement of the army in three divisions was common both among the Israelites (Judges 7:16; Judges 11:43; 1 Samuel 11:11) and their enemies (1 Samuel 13:17). Compare also 2 Kings 11:5–6; David proposed to take the chief command in person.