The Moresby Treaty was an anti-slavery treaty made between Sayyid Said, Sultan of Muscat and Oman and Fairfax Moresby, senior officer of Mauritius, on behalf of Britain in September 1822.Initially composed of six articles, the purpose of the treaty was to limit the Indian Ocean slave trade by preventing the importation of slaves to British holdings in India and the Indian Ocean from land ruled by Omani Arabs in East Africa. The treaty barred the sale of slaves to Christians of any nationality, recognized the sultan’s jurisdiction over the waters near the East African coast, allowed for the installation of a British official in Zanzibar or the mainland, and created the Moresby Line.
On December 17, 1839 the treaty was expanded in scope, adding three more articles to the original agreement. The extension increased the area in which the transportation of slaves was considered illegal by moving the endpoint of the Moresby Line west to the port of Pasni on the Makran Coast. Additionally, the amendment prohibited the sale of Somalis as slaves because, as Muslims, they were considered ‘free men’ by the Omani ruler who was a Muslim himself.