Manuel was with the Turkish army at Brousa when he learned the death of his father in 1391. He escaped secretly, hastened to Constantinople, and succeeded in being proclaimed as the sole occupant of the imperial throne. Bajazed, who had become sultan on the assassination of his father, Murad, in 1389, taken by surprise at the escape of his hostage, at once presented alarming demands. He asked that the Turks should have a resident cadi within Constantinople itself and that Manuel should declare himself to be the sultan’s vassal and pay tribute. After a year of fruitless negotiations, which Manuel had protracted in order that he might send to the West to implore aid, Bajazed attacked the empire on every side. Within a few months Turks were pillaging the Adriatic coast, were exterminating or carrying off prisoners from Thrace, and were laying siege to the capital. Their leader before the city urged the citizens to declare for Manuel’s nephew, John, the son of Andronicus, who had, indeed, been compelled by Bajazed to come forward as a pretender. In 1395 John joined the Turks in attacking the capital, but was defeated. The Turkish leader returned across the Bosporus, strengthened his position on the Gulf of Ismidt, by building a castle or fortress, probably the one now seen at Guebseh, and another on the Bosporus known as Guzel-hissar,[97] and then once more summoned Manuel to surrender the city. Thereupon the emperor took a step which, if the version of Ducas is correct, justifies his historian for attributing it to wisdom and patriotism. He arranged to share the empire with John, to leave the city himself, and to allow him to enter on condition that he would not hand it over to the Turks. John, however, on his side had agreed with Bajazed that Selymbria and the other places on the north shore of the Marmora which he had held since the death of his father should be delivered to the Turks, and, this arrangement being concluded, the city was saved from attack.[98] Meantime the spread of the Turks over new territories once more alarmed the West, and in 1394 Boniface preached a Crusade and urged in what is now Austria and the states of Venice that immediate action should be taken against them. The danger was pressing and the pope’s call to battle was this time responded to. Sigismund, the Hungarian king, informed the emperor that he had fifty-two thousand armed men, and invited his co-operation. [Sidenote: Battle of Nicopolis, 1396.]