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In page Moscow:

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The first known reference to Moscow was in 1147, as a meeting place of Yuri Dolgorukiy and Sviatoslav Olgovich. At the time it was a minor town on the western border of Vladimir-Suzdal Principality.[1] In 1156, Dolgorukiy fortified the town by creating a wooden wall; this structure became the Kremlin.[2] In the course of the Mongol invasion of Kievan Rus', the Mongols under Batu Khan burned the city to the ground and killed its inhabitants.[citation needed]