In Genghis Khan's military system, a tumen was recursively built from units of 10 (aravt), 100 (zuut) and 1,000 (mingghan), each with a leader reporting to the next higher level. Tumens were considered a practical size, neither too small for an effective campaign nor too big for efficient transport and supply. The military strategy was based on the use of tumens as a useful building block causing reasonable shock and attack. A Mongol army usually consisted out of three tumen, but armies consisting of only one tumen were also deployed. Regardless, tumen would often be understrength and the number of tumen deployed doesn't provide an accurate number of combatants.