The grant of Roman citizenship to practically all freemen in the provinces by Caracalla in 212 was therefore a severe blow to Italy, because it raised the provinces to the level of the peninsula, and paved the way for Diocletian to apply his fiscal reforms to the whole Roman world.[22] His system of taxation was one of the most complete and methodical that has ever been known. We can speak of only a few of its salient features here. The population was divided into three classes, the owners of land or other property, merchants, and laborers. For the first class, the class most important for the purpose of taxation, the fiscal unit was the _caput_ or _iugum_. The _caput_ was the working power of a man in good health. A _iugum_ was a piece of land from which a fixed return might be expected. The number of _capita_ and _iuga_ was determined by a careful census at fixed intervals, and each land owner paid according to the number of laborers and _iuga_ on his estate. The tax paid by merchants depended on the capital invested in their business. Laborers paid a poll tax. The plan was well thought out, but the failure of the government to reduce the valuation of property as the prosperity of the empire declined, and its inability to reduce its own expenses made the taxes an intolerable burden, and contributed largely to impoverish the people and ruin local self-government. The Roman system of taxation, with some modifications, continued in use after the dissolution of the Empire and exerts an influence on our modern systems. Duties were still collected on wares in transit at frontiers, at bridges and at other points on the public highways. A quota of the produce was required from the owners of land, and the property of those who died without leaving a will went to the crown. It is clear that most of the Roman taxes, for instance, customs duties, the inheritance tax, a tax on landed property, and a poll tax, have been taken over by us, and find a place in our modern systems of taxation.