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In page Rzeszów:

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In the 7th century, the first Slavs appeared in the area, which is confirmed by numerous archaeological findings.[citation needed] Most probably, Rzeszów was then inhabited by the Vistulans. In the 10th century, it became part of the emerging Duchy of Poland. Sometime between 11th and 13th century the town was conquered and subsequently annexed by the East Slavic Ruthenians from the weakened and fragmented Polish state (see Testament of Bolesław III Wrymouth).