Fresh trouble arose in Granada, for Pedro of Castile came to the assistance of the lawful ruler. But Mohammed, witnessing the ravage of the district by the Christian army, was far from receiving the invader with open arms. "For no empire in the world would I sacrifice my country," cried the sultan. Thereupon the King of Castile retired, and Abu Saïd, mistaking the reason of his return to Seville, went thither to beg his alliance. The story of the sultan's murder, at the instigation of Pedro the Cruel, has often been told. Abu Saïd was done to death at Seville, and the resplendent ruby which was taken from him was presented to the Black Prince of England, and is still preserved among the regalia of England. Mohammed then returned to his capital. With the exception of a rebellion under Ali Ben Nasr, he passed twenty years of peace. Granada became a more thriving city, and under the sultan's clement administration, it was the resort of traders of all nations and the centre of culture in the south. According to Mendoza, the inhabitants of Granada numbered about 420,000 in the reign of Mohammed V., but it is probable that the number was wildly over-estimated. [Illustration: GRANADA--THE ALHAMBRA: THE AQUEDUCT] Yusuf II. followed Mohammed V. He was suspected of favouring the Christians. He certainly released all the captives of that faith, and restored them to their own country. This act appears to have incited his son Mohammed to rise against the throne. Yusuf was at first disposed to relinquish his sovereignty, for he was a lover of peace; but on the advice of an ambassador from Morocco he raised an army and advanced on Murcia. At this period the King of Castile was Enrique III., an incapable monarch in defiance of whose orders Don Martin de la Barbuda, the Master of Calatrava, headed an advance into the kingdom of Yusuf. The force was, however, entirely routed by the Moors. Soon after (1395) Yusuf, the pacific sovereign, was dead--the victim, it is said, of a poisoned potion, in the form of a tonic sent him by the Sultan of Fez.