The Geledi Sultans were at the height of their power. They dominated the East African ivory trade, and also held sway over the Jubba and Shebelle valleys in the hinterland. The Omani Sultans' authority in Mogadishu, however, was largely nominal (existing by name only). When Imam Azzan bin Qais of Oman sought to build a fort in the city, he was thus obligated to request permission from Sultan Ahmed Yusuf the real power broker who in turn convinced the Hiraab Imam to acquiesce to the decision. Omani and later Zanzibari officials were mere representatives of the Sultan to collect customs and needed the fort for their own security rather than control of the city. This Fort of Garessa was eventually constructed in 1870. The Sultan of Zanzibar later leased and then sold the infrastructure that he had built to the Italians, but not the land itself, which was Somali owned.