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In page Carrara:

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In the early Middle Ages it was a Byzantine and then Lombard possession, and then, it was under the Bishops of Luni who started to write the city's history when the Emperor Otto I gave it to them.[2] It turned itself into a city-state in the early 13th century; during the struggle between Guelphs and Ghibellines, Carrara usually belonged to the latter party. The Bishops acquired it again in 1230, their rule ending in 1313, when the city was given in succession to the Republics of Pisa, Lucca and Florence. Later it was acquired by Gian Galeazzo Visconti of Milan.