school. By the beginning of the 16th century, Katsina had become a very important commercial and academic center in Hausaland, and Gobarau Mosque had grown into a famed Islamic institution of higher learning. Gobarau continued to be Katsina's central mosque until the beginning of the 19th century AD. Yoruba The Yoruba surrounded their settlements with massive mud walls. Their buildings had a similar plan to the Ashanti shrines, but with verandahs around the court. The walls were of puddled mud and palm oil. The most famous of the Yoruba fortifications, and the second largest wall edifice in Africa, is Sungbo's Eredo, a structure that was built in honour of a traditional oloye by the name of Bilikisu Sungbo, in the 9th, 10th and 11th centuries. The structure is made up of sprawling mud walls among the valleys that surrounded the town of Ijebu-Ode in Ogun State. Sungbo's Eredo is the largest pre-colonial monument in Africa, larger than the Great Pyramids or Great Zimbabwe. Eastern Africa Burundi Burundi never had a fixed capital. The closest thing to it was a royal hill. When the king moved, his new location became the insago. The compound itself was enclosed inside a high fence and had two entrances. One was for herders and herds. The other was to the royal palace, which was itself surrounded by a fence. The royal palace had three royal courtyards, each serving a particular function: one for herders, one as a sanctuary, and one encompassed by kitchen and granary. Ethiopia Throughout the medieval period, the monolithic influences of Aksumite architecture persisted, with its influence felt strongest in the early medieval (Late Aksumite) and Zagwe periods (when the churches of Lalibela were carved). Throughout the medieval period, and especially during the 10th to 12th centuries, churches were hewn out of rock throughout Ethiopia, especially in the northernmost region of Tigray, which was the heart of the Aksumite Empire. However, rock-hewn churches have been found as far south as Adadi Maryam (15th century), about south of Addis Ababa. The most famous examples of Ethiopian rock-hewn architecture are the 11 monolithic churches of Lalibela, carved out of the red volcanic tuff found around the town. Although later medieval hagiographies attribute all 11 structures to the eponymous king Lalibela (the town was called Roha and Adefa before his reign), new evidence indicates that they may have been built separately over a period of