152 A TROPICAL DEPENDENCY reached its greatest prosperity. Mansa Suleiman reigned for twenty-four years, but he was succeeded by Mansa Djata, a vicious tyrant, during whose reign of fourteen years the decadence of the kingdom began. Mansa Djata, far from practising the frugality of his ancestors, had a passion for expenditure which he carried to madness. He spent, it is said, in every kind of folly and debauchery, the immense wealth which had been amassed by the kings his predecessors. It was this king who sold the famous nugget which was regarded, we are told, as one of the rarest of the public treasures. He died finally of sleepingsickness. Ibn Khaldun describes the malady as being very common in the country, but as this is the first instance which we have of it historically, the symptoms as then recognised are perhaps worth noting. It was specially apt, Ibn Khaldun says, to attack the upper classes of the people. It began by periodic attacks, and finally brought the patient to such a state that he could not remain awake for a moment. It then declared itself permanently, and ended sooner or later in death. The King Djata suffered for two years from periodic attacks before he died in 1374-This was practically the end of the kingdom of Melle. The Songhay kingdom had already asserted its independence in 1355, within two years of Ibn Batuta's visit. The Tuaregs took Timbuctoo in 1434. In 1468 the overthrow of the empire was begun by Sonni Ali, the Songhay precursor of the great dynasty of the Askias, and the conquest of Melle by the Songhays was completed in a twelve years' war carried on by Askia the Great, from 1 501 to 15 13. It is interesting to note that in this very year, 15 13, a map was published in Strasburg in which the kingdom of Melle appears under the title of Regnum Musa Melle de Ginovia.