The ruin of the South Serbians and Eastern Bulgarians of which Ducas speaks had really taken place. They had each ventured to declare themselves empires. With the indifference which characterises the Greek writers in regard to the conduct of other nations, they allude to rather than mention how that ruin had been brought about. In 1371, a great battle took place on the plains of the river Maritza which sealed the fate of the Eastern Bulgarians and of the Serbians who were in Macedonia. The three sons of the kral took advantage of the absence of Murad in Asia and, having collected an army of sixty thousand men, marched almost as far as Adrianople without opposition. While they were feasting in front of a bridge over the Maritza near Harmanli, fully assured of their safety by reason of their superiority in numbers, suddenly a night attack was made upon them by a small division of the Turkish army. It was soon joined by the entire army of seventy thousand Turks. Wild confusion was followed by a terrible slaughter. One of the three sons of the kral was killed and the other two were drowned in the Maritza. Hundreds of soldiers perished in attempting to cross it. The army was simply annihilated.[92] To assist him in his conquest of Hungary, Serbia, Bulgaria, and Moldavia, Murad allied himself, in 1373, with the Tartars north of the Danube, and both prepared to attack these states. Meanwhile in the troubles which arose in 1374 between John and his son Manuel on the one side and Andronicus the grandson of John by his eldest son of the same name, Murad exercised his right as suzerain. Shortly after Manuel was associated with his father, the two were ordered to accompany their lord on an expedition. It was during their absence that the eldest sons of the emperor and sultan, as already mentioned, either swore friendship and common action, when each succeeded to his father’s throne, or were considered by their fathers to have done so. It may have been believed that they had entered into a conspiracy to hasten such succession. Countouz, the obnoxious son of Murad, raised a rebellion against his father when he heard of his cruel resolve, but his troops passed over to the side of their sultan. He fled to Didymotica and joined Andronicus, who was also a fugitive from his father. Murad followed his son, and laid siege to that city. The inhabitants, pressed by famine, opened the gates to him. Countouz was blinded by his father, but Andronicus escaped; all the garrison was drowned and a large number of the inhabitants had their throats cut, Murad adding to his barbarity by compelling the fathers to be the executioners of their sons.[93] [Sidenote: Philadelphia surrendered, 1379.]