Such was the structure which rested upon the purse of the taxpayer and upon a system of finance inherently vicious and wasteful. The main support of the treasury was still, as it had always been, the land tax, known as the _capitatio terrena_, the old _tributum soli_. It was the landed proprietor (_possessor_) who found the wherewithal to keep the Empire on its feet. Diocletian had reorganised the census, and, in the interests of the treasury, had caused a new survey and inventory to be made of practically every acre of land in every province. By an ingenious device he had established a system of taxable units (_jugum_ or _caput_), each of which paid the round sum of 100,000 sesterces or 1000 aurei. The unit might be made up of all sorts of land—arable, pasture, or forest—the value of each being estimated on a regular scale. Thus five acres of vineyard constituted a unit and were held to be equivalent to twenty acres of the best arable land, forty acres of second-class land, and sixty of third-class. Nothing escaped: even the roughest woodland or moorland was assessed at the rate of four hundred and fifty acres to the unit. The Emperor and his finance ministers estimated every year how much was required for the current expenses of the Empire. When the amount was fixed, they sent word throughout the provinces, and the various municipal curiæ, or town senates, knew what their share would be, for each town and district was assessed at so many thousand units, and each curia or senate was responsible for the money being raised. The curia was composed of a number of the richest landowners, who had to collect the tax from themselves and their neighbours as best they could. If, therefore, any _possessor_ became bankrupt, the others had to make up the shortage between them. Those who were solvent had to pay for the insolvent. All loopholes of evasion were carefully closed. Landowners were not permitted to quit their district without special leave from the governor; they could not join the army or enter the civil service. When it was found that large numbers were becoming ordained in the Christian Church to escape their obligations, an edict was issued forbidding it. Once a decurion always a decurion.