The conclusion as to the strength of the army in the first years of the republic, before the latter had acquired any considerable accession of territory, corresponds closely with a moderate estimate of the population under the conditions then existing. The area of the state was about 983 square kilometers (equivalent to 379.5 sq. mi. or 242,899 acres).[486] Estimating the population of this agricultural community at its maximum of sixty to the square kilometer, we should have less than 60,000 for the entire area.[487] The number of men from seventeen to sixty, the Roman military age, should be about thirty per cent of the population[488]—less therefore than 18,000. If the ratio of juniors to seniors was about three to one,[489] we should have about 13,000 juniors to 5000 seniors. But a deduction must be made for slaves and for the physically incapacitated, leaving perhaps 9000 or 10,000 juniors and 3000 or 4000 seniors. These results are not unreasonable. Making allowance for several hundred supernumeraries,[490] we should then have no more than enough juniors to fill the eighty-four centuries of foot and the six troops of horse. It is clear, therefore, that all available forces were included in the army and that the junior centuries could not have contained more than a hundred men each. Even before the phalanx had thus been brought to perfection, modifications were being made in the equipment under the influence of the Gallic invasion.[491] The introduction of pay, about 400 B.C., as has been said,[492] broke down the distinction of equipment based on degree of wealth, and not long afterward, probably in the time of the Samnite wars, the phalanx gave way to the manipular legion, which reached its full development in the Punic wars.[493] VI. _The Five Classes and their Ratings_