involved in the trade network between India and the Mediterranean. Growing from the proto-Aksumite Iron Age period ( 4th century BCE), it rose to prominence by the 1st century CE. The Aksumites constructed monolithic stelae to cover the graves of their kings, such as King Ezana's Stele. The later Zagwe dynasty, established in the 12th century, built churches out of solid rock. These rock-hewn structures include the Church of St. George at Lalibela. In ancient Somalia, city-states flourished such as Opone, Mosyllon and Malao that competed with the Sabaeans, Parthians and Axumites for the wealthy Indo–Greco–Roman trade. In the Middle Ages several powerful Somali empires dominated the region's trade, including the Ajuran Sultanate, which excelled in hydraulic engineering and fortress building, the Sultanate of Adal, whose General Ahmed Gurey was the first African commander in history to use cannon warfare on the continent during Adal's conquest of the Ethiopian Empire, and the Geledi Sultanate, whose military dominance forced governors of the Omani empire north of the city of Lamu to pay tribute to the Somali Sultan Ahmed Yusuf. Southeast Africa According to the theory of recent African origin of modern humans, the mainstream position held within the scientific community, all humans originate from either Southeast Africa or the Horn of Africa. During the first millennium CE, Nilotic and Bantu-speaking peoples moved into the region, and the latter now account for three-quarters of Kenya's population. On the coastal section of Southeast Africa, a mixed Bantu community developed through contact with Muslim Arab and Persian traders, leading to the development of the mixed Arab, Persian and African Swahili City States. The Swahili culture that emerged from these exchanges evinces many Arab and Islamic influences not seen in traditional Bantu culture, as do the many Afro-Arab members of the Bantu Swahili people. With its original speech community centered on the coastal parts of Tanzania (particularly Zanzibar) and Kenya a seaboard referred to as the Swahili Coast the Bantu Swahili language contains many Arabic loan-words as a consequence of these interactions. The earliest Bantu inhabitants of the Southeast coast of Kenya and Tanzania encountered by these later Arab and Persian settlers have been variously identified with the trading settlements of Rhapta, Azania and Menouthias referenced in early Greek and Chinese writings from 50 CE to 500 CE. These early writings perhaps document the first wave of Bantu settlers to reach Southeast Africa during their