The primary source of direct tax revenue was individuals, who paid a poll tax and a tax on their land, construed as a tax on its produce or productive capacity. Supplemental forms could be filed by those eligible for certain exemptions; for example, Egyptian farmers could register fields as fallow and tax-exempt depending on flood patterns of the Nile. Tax obligations were determined by the census, which required each head of household to appear before the presiding official and provide a head count of his household, as well as an accounting of property he owned that was suitable for agriculture or habitation. A major source of indirect-tax revenue was the "portoria", customs and tolls on imports and exports, including among provinces. Special taxes were levied on the slave trade. Towards the end of his reign, Augustus instituted a 4% tax on the sale of slaves, which Nero shifted from the purchaser to the dealers, who responded by raising their prices. An owner who manumitted a slave paid a "freedom tax", calculated at 5% of value. An inheritance tax of 5% was assessed when Roman citizens above a certain net worth left property to anyone but members of their immediate family. Revenues from the estate tax and from a 1% sales tax on auctions went towards the veterans' pension fund "(aerarium militare)". Low taxes helped the Roman aristocracy increase their wealth, which equalled or exceeded the revenues of the central government. An emperor sometimes replenished his treasury by confiscating the estates of the "super-rich", but in the later period, the resistance of the wealthy to paying taxes was one of the factors contributing to the collapse of the Empire. With the conclusion of the Third Mithridatic War in 63 BC, the Roman Republic now incorporated the Kingdom of Pontus, Cilicia, most of Syria, and the island of Crete into its growing dominion, as well as turning the Kingdom of Judea into a client state. The Roman historian Plutarch records that after Pompey's return to Rome as a renowned conqueror of the east, tablets were presented showing that state revenues had increased from 50 million denarii to 85 million, an increase from 200 to 340 million sesterces from new taxes levied. Yet this was apparently roughly the size of the entire state budget of the Ptolemaic Kingdom of Hellenistic Egypt. Both Cicero and Strabo related how at the beginning of the reign of Ptolemy XII Auletes (80-51 BC) his kingdom received an annual revenue of 12,500 talents, the equivalent of 75 million denarii, or 300 million sesterces.