Even before the state had brought the laborer under its control, it had acquired the ownership of a great part of the natural resources of the Empire. The Emperor owned gold mines in Dalmatia and Dacia, silver mines in Pannonia, iron mines in Noricum, tin mines in Britain, and marble quarries, forests, clay-pits, and salt-works in other provinces. Egypt was from the outset the personal domain of the Emperor, and by confiscation or legacy he gradually acquired immense estates in most of the richer provinces. Most of the mines and the imperial estates were in charge of a procurator, and were let out at a fixed rental to contractors. The work on the estates was done by tenants. Whether state ownership promoted productivity or not we can not say with certainty, but the complaints which we find in the _Theodosian Code_[37] of the exorbitant prices charged for the products of the mines and quarries would seem to show that they were inefficiently managed under the later empire. The outcome, so far as the workers in the mines and the tenants on the estates are concerned, is clear enough. Titles are found in the _Theodosian Code_,[38] requiring those who live near the mines and their children to work in the mines. The condition of the tenants on imperial estates had fallen to a low point as early as the latter part of the second century, as we can see from the pathetic petition which the people on an imperial estate in Africa addressed to Commodus. In time the tenants on these estates found it impossible to give up their leases, or were forbidden to do so, and became serfs.