Page "Roman legion" Paragraph 32

Every legion had a large baggage train which included 640 mules ( 1 mule for every 8 legionaries ) only 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 15 days ' rations, for about 25 – 30 kg ( 50 – 60 pounds ) of load total.

To make this easier, he issued each legionary a cross stick 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.