the Adriatic coast; Charlemagne's own son Pepin of Italy, king of the Lombards, under the authority of his father, embarked on a siege of Venice itself. This, however, proved a costly failure. The siege lasted six months, with Pepin's army ravaged by the diseases of the local swamps and eventually forced to withdraw in 810. A few months later, Pepin himself died, apparently as a result of a disease contracted there. In the aftermath, an agreement between Charlemagne and the Byzantine Emperor Nicephorus in 814 recognized Venice as Byzantine territory, and granted the city trading rights along the Adriatic coast. In 828 the new city's prestige increased with the acquisition, from Alexandria, of relics claimed to be of St Mark the Evangelist; these were placed in the new basilica. Winged lions—visible throughout Venice—are the emblem of St Mark. The patriarchal seat was also moved to Rialto. As the community continued to develop, and as Byzantine power waned, its own autonomy grew, leading to eventual independence. Expansion From the 9th to the 12th centuries, Venice developed into a powerful maritime empire (an Italian thalassocracy known also as repubblica marinara). In addition to Venice there were seven others: the most important ones were Genoa, Pisa, and Amalfi; and the lesser known were Ragusa, Ancona, Gaeta and Noli. Its own strategic position at the head of the Adriatic made Venetian naval and commercial power almost invulnerable. With the elimination of pirates along the Dalmatian coast, the city became a flourishing trade centre between Western Europe and the rest of the world, especially with the Byzantine Empire and Asia, where its navy protected sea routes against piracy. The Republic of Venice seized a number of places on the eastern shores of the Adriatic before 1200, mostly for commercial reasons, because pirates based there were a menace to trade. The doge already possessed the titles of Duke of Dalmatia and Duke of Istria. Later mainland possessions, which extended across Lake Garda as far west as the Adda River, were known as the Terraferma; they were acquired partly as a buffer against belligerent neighbours, partly to guarantee Alpine trade routes, and partly to ensure the supply of mainland wheat (on which the city depended). In building its maritime commercial empire, Venice dominated the trade in salt, acquired control of most of the islands in the Aegean, including Crete, and Cyprus in the Mediterranean, and became a