by contingents of allied auxiliary troops, called auxilia. Auxilia contained immunes (specialist units), engineers and pioneers, artillerymen and craftsmen, service and support personnel and irregular units made up of non-citizens, mercenaries and local militia. These were usually formed into complete units such as light cavalry, light infantry or velites, and labourers. There was also a reconnaissance squad of ten or more light mounted infantry called speculatores, who could also serve as messengers or even as an early form of military intelligence service. As part of the Marian reforms, the legions' internal organisation was standardised. Each legion was divided into cohorts. Prior to this, cohorts had been temporary administrative units or tactical task forces of several maniples, even more transitory than the legions themselves. Now the cohorts were ten permanent units, composed of six centuries and in the case of the first cohort five double strength centuries each led by a centurion assisted by an optio. The cohorts came to form the basic tactical unit of the legions. Ranking within the legion was based on length of service, with the senior centurion commanding the first century of the first cohort; he was called the primus pilus (First Spear), and reported directly to the superior officers (legates and tribuni). All career soldiers could be promoted to the higher ranks in recognition of exceptional acts of bravery or valour. A newly promoted junior centurion would be assigned to the sixth century of the tenth cohort and slowly progressed through the ranks from there. Every legion had a large baggage train, which included 640 mules (one mule for every eight legionaries) just for the soldiers' equipment. To keep these baggage trains from becoming too large and slow, Marius had each infantryman carry as much of his own equipment as he could, including his own armour, weapons and five days' rations, for about 25–30 kg (50–60 pounds) of load total. To make this easier, he issued each legionary a cross stick (furca) to carry their loads on their shoulders. The soldiers were nicknamed "Marius' Mules" because of the amount of gear they had to carry themselves. This arrangement allowed for the possibility for the supply train to become temporarily detached from the main body of the legion, thus greatly increasing the army's speed when needed. A typical legion of this period had 5,120 legionaries as well as a large number of camp followers, servants and