Almost all the details we know of the extraordinarii are described to us in "The Histories" of the ancient Greek historian Polybius. The standard Consular army of the Republic was made up of two legions and a comparable number of Italian allied troops, termed the alae. In theory, the alae would be the same size as the legions, except for the cavalry, which was tripled; so, a standard ala would contain about 900 cavalry and 4,200 foot. In practice, there was often more allied infantry than Roman infantry; for instance, the four legions (numbering 15,000 Roman infantry) were supported by 20,000 allied infantry at the Battle of the Trebia.