According to Ethiopian Muslims, after Mecca, Medina and Jerusalem, Harar used to be the forth holy city of Islam. It still is a center of Islamic study and devotion. In the ancient walled city, 82 mosques can be found. It has 102, often centuries-old shrines, in which outstanding Muslims are buried. For centuries, Harar was ruled by Sultans. It was a stopover for caravans that were on their way from the Red Sea to the interior of the country and the continent. The dromedaries transported ivory, coffee, tobacco, and slaves were also taken. Merchants from Oman and Yemen loved to come to the city. Like many ancient cities in Europe, Harar had its own currency and the use of foreign money was forbidden. Jugol the city wall was constructed by the 42nd Amir of the 72 that ruled Harar, Amir Nur, between 1559 and 1567. After the completion of the wall Harar became a free and self-governing city for three generations.