the duchy. It lost Brondolo and Fossone, to the south of the Lagoon of Venice. Both were important for their saltworks and were on the inland trade waterways of the rivers Brenta and Adige. The border north of Cittanova, from where the routes to northern Europe started, was no longer defined, which led to disputes and to a long fight that doge Pietro II Orseolo (991-1009) undertook in 995–96 against the belligerent bishop of Belluno. A new tax which increased the tax burden on goods was introduced. In 971 the Byzantine emperor John I Tzimisces imposed a ban on the sale military material (wood and weapons) to the Arabs. Ships that breached this and the men and goods they carried would be burned. This was aimed against the Fatimid Caliphate, as a war between the empire and the califate broke out again in that year. Pietro complied, but this undermined Venice's economic interests as trade with the Arab coast of North Africa, which was short of wood, was an important part of Venetian trade. Wood for furnishing was excluded from the ban, but this was of little relief. The ban was not instituted by a decree of the doge, but by an oath (carta promissiones) by the popular assembly to abstain from the banned acts with a penal clause regarding breaches chosen freely by the assembly. The fact that the ban was adopted by the will of the popular assembly, rather than by a ducal decree crystallised the gulf that had developed between the doge and the people and the isolation of the former from the latter. Cessi sees this as a legislative overturning. It was a precursor to the shift in the balance of power between the doge and the people which was to lead to the formation of the Venetian Republic in the 12th century and the custom of the doge giving a ducal promissio (promissio domini ducis), an oath, on assuming power to be loyal to the Republic and to recognise the limitations to his powers created by the Republic. In 976 the people of Venice rebelled against Pietro. Betrolini argues that there was discontent with Pietro's foreign policy. The relations with Otto I led to economic sacrifices. The economic repercussions of the Byzantine ban increased animosity. His favouritism for his relatives was disliked. Norwich sees Pietro having become too powerful as the cause. His acquisition, though