The opposition [he said] must be ended; these barriers must be removed. It was for them to complete the work of their fathers. They had now against them a single city, one which could not resist their attacks; a city whose population was greatly reduced and whose former wealth had been diminished by Turkish sieges, and by the continued incursions made by his ancestors upon its territories; a city which was now only one in name, for in reality its buildings were useless and its walls abandoned and for the great part in ruins. Even from its weakness, however, they knew that from its favourable position, commanding both land and sea, it had greatly hindered their progress and could still hinder it, opposing their plans and being always ready to attack them. Openly or secretly it had done all it could against them. It was the city which had brought about the attack by Timerlane and the suffering which followed. It had instigated Hunyadi to cross the Danube, and on every occasion and in every possible manner had been their great enemy. The time had now come when, in his opinion, it should be captured or wiped off the face of the earth. One of two things: he would either have it within his Empire or he would lose both. With Constantinople in his possession, the territories already gained could be safely held and more would be obtained; without it, no territory that they possessed was safe.[15] In the ensuing winter (1452) Mahomet made every preparation at Adrianople for a campaign in the next year. Having no means of casting cannons, which at that time were coming into use in European armies, he tempted a Wallachian, who was experienced in such work, and who was in the service of the Greeks, to come over to his side for higher pay, and devised with him a cannon of enormous size, firing stone balls of 2½ feet in diameter, and many other smaller, but still large, guns throwing balls of 150 lb. weight, for use against the walls of Constantinople. He also constructed a large fleet of war vessels propelled by oars, biremes and triremes, to be used in the siege of the city. He was most active and eager, working day and night in concerting plans with his generals for his great purpose. Early in the following year (1453) he collected in front of the walls of Constantinople an army, estimated at a hundred and fifty thousand men, including twelve thousand Janissaries, and a vast number of irregulars and camp followers eager for the sack of the great city.