in Gao the flood lasts longer and reaches a maximum in December. There is a large year-to-year variation in the extent of the flooding. The existing and proposed dams upstream of Gao reduce the overall flow of the river and could potentially have a large effect on the local agriculture. When in flood the river is 4 km wide at Gao but during the dry season a number of islands appear in the river. There is very little flow, only 5% of the maximum, in June and July. History Early Middle Ages The history of the Gao Empire precedes that of the Songhai Empire in the region of the Middle Niger. Both empires had the town of Gao as their capital. Apart from some Arabic epitaphs on tombstones discovered in 1939 at the cemetery of Gao-Saney (6 km to the east of the city) there are no surviving indigenous written records that date from before the middle of the 17th century. Our knowledge of the early history of the town relies on the writings of Arabic geographers living in Morocco, Egypt and Andalusia, most of whom never visited the region. These authors referred to the town as Kawkaw or Kuku. The two key 17th century chronicles, the Tarikh al-Sudan and the Tarikh al-fattash, provide information on the town at the time of the Songhai Empire but they contain relatively little on the social and economic history. The chronicles do not, in general, acknowledge their sources. Their accounts for the earlier periods are almost certainly based on oral tradition and for events before the second half of the 15th century they are likely to be less reliable. For these earlier periods, the two chronicles sometimes provide conflicting information. The earliest mention of Gao is by al-Khwārizmī who wrote in the first half of the 9th century when Gao was already an important regional power. Al-Yaqubi wrote in his Tarikh in around 872: There is the kingdom of the Kawkaw, which is the greatest of the realms of the Sūdān, the most important and most powerful. All the kingdoms obey its king. Al-Kawkaw is the name of the town. Besides this there are a number of kingdoms of which the rulers pay allegiance to him and acknowledge his sovereignty, although they are kings in their own lands. Ibn al-Faqih (writing c. 903) mentions a caravan route from Egypt to ancient Ghana via