John himself was in serious difficulties with the Ottoman sultan, Murad. These two sovereigns were now, indeed, the two great actors on the stage during several years, but the character of Murad dominated over that of the commonplace John. To avoid possible treachery, the Christian emperor, who was not trusted by Murad, was in 1374 compelled with his son Manuel to follow the sultan in a campaign. During his absence he entrusted the government to Andronicus, his eldest son. Thereupon an accident occurred which seems greatly to have impressed contemporaries. Andronicus entered into an arrangement with the son of Murad by which the two swore to be friends and to act together, when one should become emperor and the other sultan. A definite arrangement may well be doubted and possibly all that passed was due to the impulsiveness of boyish friendship without any likelihood of practical result. Murad, however, when he heard of the agreement, blinded his son, insisted that John should treat Andronicus in the same manner, and threatened war if he did not comply. According to Ducas, John blinded not only Andronicus, but also his infant son.[81] Probably the sight of one eye only was destroyed. Andronicus was imprisoned in the Tower of Anemas with his wife and son, and John’s younger son, Manuel, was crowned as co-emperor. Two years afterwards Andronicus escaped to the Genoese in Galata. With their aid he succeeded in entering Constantinople, proclaimed himself emperor, and shut up his father in the same prison in which he had himself been confined. Two years afterwards the prisoner escaped to Scutari, and Andronicus had the sense to avoid civil war by coming to an arrangement with his father by which John was once more placed on the throne with his son Manuel. Andronicus in compensation received certain of the towns on the north side of the shore of the Marmora. When Andronicus had succeeded in obtaining possession of the city with the aid of the Genoese, almost his first act was to arrest all the Venetians, with whom the Genoese were again at war. With their aid, John endeavoured to take Tenedos from his enemies, but failed. In the following year (1379) the Genoese united themselves with Louis of Hungary and defeated the Venetians at sea. They were still sufficiently influential in 1382 to compel the emperor to make peace with Andronicus.[82] Constantly strengthening themselves, they entered into a treaty in 1387 with the Bulgarian prince of the Dobrutcha.