A.T. Robertson Commentary Mark 6:39

"And he commanded them that all should sit down by companies upon the green grass." — Mark 6:39 (ASV)

By companies (συμποσια συμποσια). Distribution expressed by repetition as in Mr 6:7 (δυο δυο) instead of using ανα or κατα. Literally our word symposium and originally a drinking party, Latin convivium, then the party of guests of any kind without the notion of drinking. So in Plutarch and the LXX (especially I Macca.).

Upon the green grass (επ τω χλωρω χορτω). Another Markan touch. It was passover time (John 6:4) and the afternoon sun shone upon the orderly groups upon the green spring grass. See on Mt 14:15. They may have been seated like companies at tables, open at one end.