All first-cohort centurions outranked all centurions from other cohorts. Legions could contain as many as 6,000 fighting men divided among several cohorts. Elderhood refers to those individuals who live past the life expectancy of their birth cohorts. The old legions were broken up into cohorts or even smaller units. These were based around four cohorts of Batavians and two cohorts of Tungrian swordsmen. In the second through tenth cohorts there were six centuria of 80 men each. In natural soils many different cohorts, or groups of microorganisms exist. He found similar overall levels of attainment between the two cohorts. Each legion was divided into "cohorts". However, these were met by the Roman garrisons which had 22 cohorts. The internal organization of a legion consisted of 10 cohorts of 6 centuries each. By AD 23, there were nine Praetorian cohorts in existence. During the experiment the three different cohorts scored differently. A variety of strategies are open to institutions where cohorts are not of sufficient size. One legion was made up of 10 cohorts.