342 THE HISTORY OF MEDIEVAL EUROPE Pietro Orseolo II (983-1008), by clearing the Adriatic of pirates; the other two by their activity against the Sara- cens whom in 1015 they drove out of the island of Sardinia. That already at this early date the Venetians were engaged in transporting wares of the Far East to European lands north of the Alps is indicated by a passage in which the German chronicler Thietmar, of the eleventh century, be- wails the shipwreck in 1017 of four Venetian vessels laden with spices. Since we know rather more of the earliest period of Venetian history than we do of that of other Italian towns, Origins of since its institutions and culture were unique, Venice anc j s i nce it became the leading medieval sea power, we shall speak first of it in this chapter. Situated on a number of small islands or banks of mud in a lagoon a little north of the mouths of the Po and Adige Rivers, Venice was secure from attack either by land or sea. The original scanty population of fisher-folk was gradually aug- mented by fugitives from the successive waves of barbarian invasion that swept over northern Italy. Theodoric the East Goth sought the aid of these islanders in transporting supplies across the Adriatic from Istria; and Belisarius, the great general of Justinian, made use of their boats in the siege of Ravenna. In 697 they are said to have elected their first doge, a single ruler for life, in place of the twelve trib- unes representing as many island communities. The doge seems to have been much like the elected kings of the Ger- man tribes. He tried to associate his son with himself in the government and thus secure his succession to the office and alter the. headship from an elective to a hereditary one. On the other hand, many a doge was slain by some rival, much as kings were in the German states in the West, or was blinded in Byzantine fashion, so that the life tenure of the position was often of short duration. Charlemagne, although master of Lombardy, had to leave Venice to the Byzantine emperor. At about this time, too, the dwellers in the lagoon concentrated their population and made their capital in the central group of islands called the Rialto,
