The "Vanguard" is a position taken up by a player, utilising a legion to surround his/her person with tightly-knit and well organised ranks. The legion must be of a certain minimum size (twenty individuals) for the vanguard to be effective. While in this vanguard position, also known as the command-post of the legion, the individual will be protected by the legionnaires against most direct forms of attack: it will be impossible to engage the individual in simple melee, it will be difficult even for projectiles to strike home. Instead the surrounding legion will need to be defeated beforehand; then the command-post will be exposed and the commander will be liable to attack.
It should be noted that while in "vanguard" position, at the command-post, the commander will be likewise restricted from direct melee against those beyond the confines of the surrounding legion; and also restricted from utilising projectiles/ranged attacks for fear of striking the encircling legionnaires. There are some methods of getting into the centre of the legion WITH the commander, alongside him or her at the command-post. This will suddenly allow for melee and other strikes to be made against the commander but, in the blink of an eye, the attacker will find all the legionnaires turned against him/her in battle. This large-scale, group engagement tends to resolve itself very quickly: bish-bash-bosh and the invading attacker is usually slaughtered.
See HELP COMMANDER for detailed information on the command-post and the role of legion commander.