 He already evolved plans to betroth his younger brother Philip to Isaac's daughter Princess Irene Angelina —deliberately or not— opening up a perspective to unite the Western and Eastern Empire under Hohenstaufen rule.According to the contemporary historian Niketas Choniates his legates were able to collect a large tribute from Isaac's brother and successor Alexios III, which, however, was not paid before Henry's death.Emperor Henry came down to earth, when an armistice between Pisa and the Republic of Venice ended and the Pisan navy immediately entered the Adriatic to attack the Venetian harbour of Pola (Pula), where they suffered a disastrous defeat.