The phrase ‘right hand man’ is a memory of fighting in a shield wall. Most warriors were right handed, and when they raised their sword arm to strike a blow, they exposed their ribs to the thrust of a spear or an enemy sword. The defensive role of the right-hand man was therefore critical, but it also produced another effect. In a shield wall, warriors also pushed their comrades forward, especially if their shields were tight together ‘rim to boss’, and this made battle fronts move to the right, wheeling like rugby scrums sometimes do.
Right-hand men have a different supporting role in modern society. Perhaps it is not accidental that the best man at a wedding ceremony traditionally stands ot the right of the groom.
Both the Ancient Greeks and Romans used this battle formation. The Roman formation is known as testudo, meaning tortoise!