Another object of the tribes, referred to Servius by our sources, was the collection of taxes.[351] We know that they afterward served this purpose; and the ancient writers, who could have had no direct knowledge of the intentions of Servius but who assigned to him without hesitation all the later developments of his organization, were in this case especially misled by their false derivation of tributum from tribus or _vice versa_.[352] A brief study of the facts in the case will prove their inference to be wrong. The most obvious consideration is that had Servius intended the tribes for the levy of taxes as well as for military purposes, he would have included all who were subject to taxation as well as all who were liable to service in the army, whereas in fact he admitted those only who were to serve. It is to be noted that primitive Rome imposed no regular direct taxes on the citizens in general. Every man equipped himself for war even after the introduction of the phalanx;[353] doubtless at first the knights provided their own horses;[354] and in short campaigns the soldiers carried their provisions from their own farms.[355] Fortifications and public buildings were erected by forced task-work. The king supported himself partly by gifts from his subjects and partly from the public property, including land.[356] Other early sources of revenue were tolls levied for the use of harbors, boundaries, temples, bridges, roads, sewers, and salt works.[357] In time the idea arose, too, that the person who did not perform military service should help with his property in the defence of the country. The estates of widows and orphans were accordingly taxed to support the horses of the knights.[358] Those men, also, who were exempt from service because they possessed no land[359] and yet had other property were required to pay on it a regular tax. From this connection with the public treasury (aerarium) they were termed aerarii. This class comprised shopkeepers and merchants. Sometimes the censors assigned to it as a punishment men who owned land. The fact that such persons were at the same time removed from their tribes is sufficient proof that the aerarii were originally outside these associations.[360] The cives sine suffragio, or Caerites, after this class had come into existence in 353, were like the aerarii in (1) that they did not belong to the tribes, (2) that they paid a regular tax, (3) that men were placed on their list as a punishment. They may accordingly be regarded as a special class of aerarii, enrolled as they were in a distinct list.[361] Whereas the cives sine suffragio either wholly lacked the franchise, as the phrase implies, or at most had but the right of the Latins,[362] the other aerarii must have voted in the proletarian century.[363]