Chad. Initial sources of slaves were the Toubou people, but by the 1st century CE, the Garmentes were obtaining slaves from modern day Niger and Chad. In the early Roman Empire, the city of Lepcis established a slave market to buy and sell slaves from the African interior. The empire imposed customs tax on the trade of slaves. In 5th century AD, Roman Carthage was trading in black slaves brought across the Sahara. Black slaves seem to have been valued in the Mediterranean as household slaves for their exotic appearance. Some historians argue that the scale of slave trade in this period may have been higher than medieval times due to high demand of slaves in the Roman Empire. Introduction of the camel Herodotus had spoken of the Garamantes hunting the Ethiopian Troglodytes with their chariots; this account was associated with depictions of horses drawing chariots in contemporary cave art in southern Morocco and the Fezzan, giving origin to a theory that the Garamantes, or some other Saharan people, had created chariot routes to provide Rome and Carthage with gold and ivory. However, it has been argued that no horse skeletons have been found dating from this early period in the region, and chariots would have been unlikely vehicles for trading purposes due to their small capacity. The earliest evidence for domesticated camels in the region dates from the 3rd century. Used by the Berber people, they enabled more regular contact across the entire width of the Sahara, but regular trade routes did not develop until the beginnings of the Islamic conversion of West Africa in the 7th and 8th centuries. Two main trade routes developed. The first ran through the western desert from modern Morocco to the Niger Bend, the second from modern Tunisia to the Lake Chad area. These stretches were relatively short and had the essential network of occasional oases that established the routing as inexorably as pins in a map. Further east of the Fezzan with its trade route through the valley of Kaouar to Lake Chad, Libya was impassable due to its lack of oases and fierce sandstorms. A route from the Niger Bend to Egypt was abandoned in the 10th century due to its dangers. Spread of Islam Several trade routes became established, perhaps the most important terminating in Sijilmasa (Morocco) and Ifriqiya to the north. There, and in other North African cities, Berber