We have already learned that the native sobas were handed over to the mercy of individual “conquistadores,” and Rebello de Aragão declares that these sobas were being “robbed and maltreated.” They were required by their masters to pay a tax in slaves, to furnish carriers, and render all kinds of services,[460] without payment. In addition to this the Governor, D. M. P. Forjaz, imposed upon them a poll-tax, which produced from twelve to thirteen thousand cruzados (say £1,650[461]) a year. Rebello de Aragão maintains that the native wars were largely due to this pernicious system, which enriched the Governor and his officials, whilst traders were made to suffer, and ceased to visit the “feiras” because of the extortionate demands made upon them. At Mpinda nearly all the “honest” trade had passed into the hands of the Dutch, because of the monopoly conferred upon Portuguese slave-dealers. He declares that a tax of 20 per cent. on the salt mined at Ndemba would pay all the legitimate expenses of government; but that, although the export duty on slaves yielded from five to six thousand cruzados, there had not yet been built a decent house for the government offices. Garcia Mendes Castellobranco, in a memoir[462] addressed to the King in 1620, is equally outspoken with regard to the treatment of the native chiefs, who, he maintains, ought not to be taxed more heavily than at the time when they were still subjects of a native king. He, too, refers to the salt mines as a source of revenue, recommends the levying of a toll at river crossings, and the expropriation of the uncultivated territory around S. Paulo.[463] Many of these abuses may, no doubt, be traced to the demoralising influence of the slave-trade and the insufficient pay of the officials. A slave costing £3 7_s._ in the interior (or nothing, if taken in the course of one of the frequent slave raids) was sold for more than double that sum on the coast; and whilst money could be made thus easily the great natural resources of the country were neglected and the population—which, on the arrival of the Portuguese, is said to have been very considerable—shrank from year to year.[464] The export duties on slaves and ivory were farmed out in 1607 to one Duarte Dias Enriques for twenty million reis annually (about £6,600).[465] S. Paulo and Masanganu enjoyed municipal institutions at that time, but all outside these cities was ruled by military adventurers. The Governor (in 1607) was paid a salary of £267, but the other officials were decidedly underpaid; and thus, almost of necessity, were driven to increase their incomes by illegitimate means.[466] THE WAR WITH NGOLA NZINGA MBANDI.