You got that wrong with the Romans, Ken. Yes, in ancient times you needed your right hand free to fight of attackers. But those wouldn't attack from the middle of the road (where you would immediately detect them and they couldn't ambush you), but from the side of the road where the trees and grass were. Hence the sensibility of moving forward on the right lane where your right hand would be to the forest/bushes side.
As usual, the limeys failed to comprehend a Continental tradition.
Uwe