The remains of Stone Age cultures dating to 500,000 years ago have been found in Zimbabwe, and it is thought that the San, who still survive mostly in the Kalahari Desert of Botswana, are the last descendants of these original inhabitants of southern and central Africa. They were driven into the desert by Bantu-speaking groups during the long migrations from the north in the course of which the Bantu-speaking peoples populated much of Africa from Lake Chad to present-day South Africa. The first Bantu are thought to have reached Zimbabwe between the 5th and 10th centuries CE. Zimbabwe is home to many stone ruins, including those known as Great Zimbabwe (designated a UNESCO World Heritage site in 1986). Some ruins date from about the 9th century, although the most elaborate belong to a period after the 15th century and are of Bantu origin.Zimbabwe has 16 official languages - namely as Chewa, Chibarwe, English, Kalanga, Koi-san, Nambya, Ndau, Ndebele, Shangani, Shona, Sign Language, Sotho, Tonga, Tswana, Venda and Xhosa. However, English, Shona and Ndebele are the most widely spoken languages in the country. Approximately 70% of the population is Shona speaking and speaks ChiShona as their first language. But the official language of Zimbabwe is English.