Italy
Venice
Venice was one of the two or three great cities of late medieval Europe. By 1300 it had built a virtual empire of holdings all across the eastern Mediterranean and was certainly the richest of all European cities, yet it held no land at all on the mainland of Europe.
Venice, as you probably know, is a city built in a lagoon, partly on natural islands and partly on man-made islands. It was able to stay safe from the invasions of the earlier Middle Ages by this simple geographical fact. Another geographical fact helped make Venice rich. Its people had long been fishermen, so becoming sea-faring merchants came easily enough, but Venice is located at the northern end of the Adriatic Sea and just south of the Brenner Pass, one of the best of the passes over the Alps. As early as the 10th century the city was trading in the ports of the eastern Mediterranean and sending the goods to northern Europe.
This trade made Venice rich. It did very well out of the Crusades, winning rich concessions in ports like Constantinople, Acre, and Alexandria. Northern Europe boomed in population all through the 12th and 13th centuries, and Venice was one of the chief (but not the only) entrepôts between the North and the East. By 1300 the rivalry between Venice and Genoa for leadership in this trade was already fierce and bloody. Venice eventually emerged victorious in this struggle but not until the late 1300s.
Internally, Venice was a republic. Its first inhabitants had fled the Lombards, and when Charlemagne came across the Alps his interests were further west. The same was true for later emperors like Otto I or Henry III. Venice grew neglected by other powers. Once it began to expand it did so in directions of no interest to the western Emperors, and no one else had a navy that could match the Venetians. So the city remained independent and so remained all through our course (indeed, it remained independent until the 19th century).
It was known even our period as La Serenissima—the Most Serene Republic, a sobriquet that was consciously promoted by the city itself. It liked to pose as a republic untroubled by the factions that wracked other Italian cities, untrammeled by kings and emperors. As we'll see, this pose wasn't entirely true. In fact, we'll see its history divide across our two centuries rather neatly: in the 14th century Venice's concerns were mainly maritime; in the 15th century, Venice became more interested in affairs on the mainland. It suffered no revolutions, though, and fell to no foreign conquerors.