The Iron Warriors Legion of the late 41st Millennium is organised into a number of large warbands known as Grand Companies, each commanded by a Chaos Lord who bears the title of Warsmith. Originally, each Grand Company would have been similar in size and organisation, totaling approximately a thousand Space Marines, but now they vary in size enormously after ten millennia of battle and losses. The Warsmiths themselves are all extremely gifted in combat engineering, many maintaining a large contingent of slave-mechanicians to perform the more menial work. It is uncertain how many Grand Companies there are at any given time. At the time of the Horus Heresy, the IVth Legion had an added layer of organisation known as a Grand Battalion, which contained several Grand Companies and was commanded