You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Somalis

Context:
The birth of Islam on the opposite side of Somalia's Red Sea coast meant that Somali merchants, sailors and expatriates living in the Arabian Peninsula gradually came under the influence of the new religion through their converted Arab Muslim trading partners. With the migration of fleeing Muslim families from the Islamic world to Somalia in the early centuries of Islam and the peaceful conversion of the Somali population by Somali Muslim scholars in the following centuries, the ancient city-states eventually transformed into Islamic Mogadishu, Berbera, Zeila, Barawa and Merca, which were part of the Berberi civilization. The city of Mogadishu came to be known as the City of Islam, and controlled the East African gold trade for several centuries.

Question:
The trade of what luxury in East Africa was once centered on Mogadishu?

gold