To these measures having immediate reference to the great question of the proletariate there was added a series of enactments, which arose out of the general tendency to introduce principles milder and more accordant with the spirit of the age than the antiquated severity of the existing constitution. To this head belong the modifications in the military system. As to the length of the period of service there existed under the ancient law no other limit, except that no citizen was liable to ordinary service in the field before completing his seventeenth or after completing his forty-sixth year. When, in consequence of the occupation of Spain, the service began to become permanent,(13) it seems to have been first legally enacted that any one who had been in the field for six successive years acquired thereby a right to discharge, although this discharge did not protect him from being called out again afterwards. At a later period, perhaps about the beginning of this century, the rule arose, that a service of twenty years in the infantry or ten years in the cavalry gave exemption from further military service.(14) Gracchus renewed the rule--which presumably was often violently infringed--that no burgess should be enlisted in the army before the commencement of his eighteenth year; and also, apparently, restricted the number of campaigns requisite for full exemption from military duty. Besides, the clothing of the soldiers, the value of which had hitherto been deducted from their pay, was henceforward furnished gratuitously by the state.