A certain portion of this domain still remains, however, the property of the State and is not converted into private land. The whole of the soil which had been given in usufruct to colonies and municipal towns, is retained in its existing condition; the holders, whether Latin colonists or Roman citizens, are confirmed in their possessions; but, as the land still remains public, they are doubtless expected to continue to pay their quit-rent to the State. Similar provision is made for a peculiar class of land, which had been given by Rome as security for a national debt. The debt had never been liquidated, probably because the creditors preferred the land. This they were now to retain on condition of continued payment of the quit-rent, which marked the fact that the State was still its nominal owner. A public character is also maintained for land which had been assigned for the maintenance of roads. Here we find the only instance of an actual assignation of the Gracchan commissioners which was not converted, into private property; the obvious reason for this exception being that these occupants performed a specific and necessary duty, which would disappear if their tenure was converted into absolute ownership. Exception against ownership was also made for those commons on which the occupants of surrounding farms had an exclusive right of sending their flocks to pasture;[778] for the conversion of such grazing land into private lots would have injured the collective interests, and conferred little benefit on the individuals of the group.[779] The remaining classes of land which still remain the property of the State, are the roads of Italy, such public land as had been specially exempted from distribution by the legislation of the Gracchi, and such as had remained public on other grounds. The only known instance of the first class is the Campanian territory, which continued to be let on leases by the State and to bring to the treasury a sure and considerable revenue; the second class was probably represented by land which was not arable and had for this reason escaped distribution. The law provides that it is not to be occupied but to serve the purposes of grazing-land, and a limit is fixed to the number of cattle and sheep belonging to a single owner to which it is to afford free pasturage. For the enjoyment of grazing-rights beyond this limit dues are to be paid to the contractors who have purchased the right of collection from the State.