[291] That these conversions were not due to persecution, we know from direct historical evidence that during this vacancy of the patriarchate, the Christians had full and complete freedom of public worship, were allowed to restore their churches and even to build new ones, were freed from the restrictions that forbade them to ride on horses or mules, and were tried in law-courts of their own, while the monks were exempted from the payment of tribute and granted certain privileges. [292] How far this incident is a typical case of conversion to Islam among the Copts it is difficult to say; a parallel case of neglect is mentioned by two Capuchin missionaries who travelled up the Nile to Luxor in the seventeenth century, where they found that the Copts of Luxor had no priest, and some of them had not gone to confession or communion for fifty years. [293] Under such circumstances the decay of their numbers can readily be understood. A similar neglect probably contributed to the decay of the Nubian Church which recognised the primacy of the Jacobite Patriarch of Alexandria, as do the Abyssinians to the present day. The Nubians had been converted to Christianity about the middle of the sixth century, and retained their independence when Egypt was conquered by the Arabs; a treaty was made according to which the Nubians were to send every year three hundred and sixty slaves, with forty more for the governor of Egypt, while the Arabs were to furnish them with corn, oil and raiment. [294] In the reign of al-Muʻtaṣim (833–842), ambassadors were sent by the caliph renewing this treaty, and the king of Nubia visited the capital, where he was received with great magnificence and dismissed with costly presents. [295] In the twelfth century they were still all Christian, [296] and retained their old independence in spite of the frequent expeditions sent against them from Egypt. [297] In 1275 the nephew of the then king of Nubia obtained from the sultan of Egypt a body of troops to assist him in his revolt against his uncle, whom he by their help succeeded in deposing; in return for this assistance he had to cede the two northernmost provinces of Nubia to the sultan, and as the inhabitants elected to retain their Christian faith, an annual tribute of one dīnār for each male was imposed upon them. [298] But this Muhammadan overlordship was temporary only, and the Nubians of the ceded provinces soon reasserted their independence. [299]