rival power blocs. Roughly half of the years since independence have been marked by autocratic governments or civil war. Early history Archaeological finds show that Sierra Leone has been inhabited continuously for at least 2,500 years, populated by successive movements of peoples from other parts of Africa. The use of iron was introduced to Sierra Leone by the 9th century, and by the end of the 10th century agriculture was being practiced by coastal tribes. Sierra Leone's dense tropical rainforest partially isolated the land from other African cultures and from the spread of Islam. This made it a refuge for people escaping subjugation by the Sahelian kingdoms, violence and jihads. European contacts with Sierra Leone were among the first in West Africa. In 1462, Portuguese explorer Pedro de Sintra mapped the hills surrounding what is now Freetown Harbour, naming the oddly shaped formation Serra Lyoa (Lioness Mountain). At this time the country was inhabited by numerous politically independent native groups. Several different languages were spoken, but there was similarity of religion. In the coastal rainforest belt there were Bulom-speakers between the Sherbro and Freetown estuaries, Loko-speakers north of the Freetown estuary to the Little Scarcies River, Temne-speakers found at the mouth of the Scarcies River, and Limba-speakers farther up the Scarcies. In the hilly savannah north of all of these lands were the Susu and Fula tribes. The Susu traded regularly with the coastal peoples along river valley routes, bringing salt, clothes woven by the Fula, iron work, and gold. European contact (15th century) Portuguese ships began visiting Sierra Leone regularly in the late 15th century, and for a while they maintained a fort on the north shore of the Freetown estuary. This estuary is one of the largest natural deep-water harbours in the world, and one of the few good harbours on West Africa's surf-battered "Windward Shore" (Liberia to Senegal). It soon became a favourite destination of European mariners, to shelter and replenish drinking water. Some of the Portuguese sailors stayed permanently, trading and intermarrying with the local people. Slavery Slavery, and in particular the Atlantic slave trade, had a great effect on the region—socially, economically and politically—from the late 15th to the mid-19th centuries. There had been lucrative trans-Saharan trade of slaves in West Africa from the 6th century. At its peak (c. 1350) the Mali Empire surrounded the region of modern-day Sierra Leone and Liberia, though the