died, and his estates were annexed by the Hungarian king and divided among the Ragusan citizens Matthew, Francis, Peter, and John of Talovac (or Thallovez) as a reward for their services to Hungary. Kosača, regardless of the Turkish danger, continued his petty intrigues; he at once began to quarrel with Radosav Paulović, who was in a sense his vassal, and each made a bid for Turkish help. Ragusa attempted to mediate between them and to dissuade them from calling in the enemy, but Kosača asked for and obtained 1500 Turks to reduce Radosav to obedience.[379] In 1438 he invaded the plain of Trebinje, which was under the latter’s jurisdiction, and forced the inhabitants to fly into Ragusan territory. Later he proposed to Peter and Matthew of Talovac to attack Ragusa itself, but they refused, and the Republic on being informed intrigued against the Duke, and told the King of Hungary that he was merely an instrument of the Turks. In 1436 the Sultan Murad again invaded Bosnia, and captured Vrhbosna, which henceforth became the Turkish headquarters in the country.[380] King Tvrtko now returned with Hungarian help, but he found his whole kingdom devastated, Usora, Srebrnica, and Zvornick held by the Despot of Servia, and the rest by the Turks, or by vojvods who were Turkish vassals. He was therefore forced to agree to pay the Sultan a yearly tribute of 25,000 ducats. The real ruler of Bosnia was now Murad, who alludes to it as part of his own dominions in a privilege granted to the Ragusans in 1442, allowing them to trade “in Romania, Bulgaria, Wallachia, Servia, Albania, Bosnia, and all other lands, places, and cities under my rule.”[381] In 1440 he conquered the whole of Servia with the exception of Belgrad, which was gallantly defended by the Hungarian garrison commanded by the Ragusan Giovanni Luccari. The Sultan retired baffled, but the Despot George was forced to fly, and took refuge at Ragusa with his treasure. The following year the Sultan, Isak Beg, and the Pasha of Romania all sent to demand the surrender of the Despot, offering the Republic his treasure and an increase of territory between Cattaro and the Drina as a bribe. The citizens refused to violate the laws of hospitality,[382] but at the same time, as George was an inconvenient guest, it was hinted to him that he had better leave the city. He agreed, and suggested going to Constantinople; but the Senate dissuaded him from doing so owing to the parlous condition of the Eastern Empire. So he went to Hungary instead on a Ragusan galley.[383] Murad determined to punish the Republic for this refusal, and arrested all the Ragusans in his dominions, the ambassadors themselves escaping with difficulty to Constantinople. He then prepared to attack the city by land and sea, and the citizens strengthened their defences, increased their military forces, enlisted foreign mercenaries, and secured the services of an Italian engineer.