The mere fact that the senior century contained so few men suggests that it was not a military institution. This impression is confirmed by the information that the seniors were reserved for the defence of the city, while the juniors took the field in active service.[479] When we reflect that even in the early republic the seniors could not often have been called on for defence, as the juniors were ordinarily sufficient for the purpose,[480] that the manning of the walls did not necessarily require a division into companies or an equipment like that for field service, and that when it was thought expedient for the seniors to serve in centuries or cohorts, their enrolment in these companies is especially mentioned, our conviction that the senior centuries did not belong to the original Servian organization grows into a certainty.[481] V. _Conclusions as to the Servian and Early Republican Organizations; Transition to the Manipular Legion_ In our search for the Servian and post-Servian schemes of military organization we found it necessary to eliminate from the discriptio centuriarum all the centuries of pedites with the exception of the juniors. But even a military century of juniors could not have remained identical with a voting century; for the former comprised a fixed number and the same for all ratings, whereas in the comitia of historical time the centuries varied greatly in size, many of them containing far more than a hundred men each. In the four lower classes each century contained as many men as the entire first class;[482] and individuals constantly shifted from one class to another as their several properties increased or diminished.[483] It is a mistake, therefore, to think of the army as identical with even the junior centuries of the comitia.[484] Doubtless when the Servian army was first introduced, its organization was made to fit actual conditions, so that all who were liable to service found their place in it; but as the political assembly of centuries was instituted many years afterward, the army with its various enlargements could have kept meanwhile no more than approximate pace with the changing population, and at no time could it include the physically disqualified, who nevertheless had a right to vote in the junior centuries of the political assembly. On the other hand there were soldiers in the army too young to be in the comitia centuriata.[485]