Ostrów Tumski is an island between two branches of the river Warta in the city of Poznań in western Poland. Poznań Cathedral and other ecclesiastical buildings occupy the central part of the island. Ostrów Tumski is part of the city's former Nowe Miasto district, although it is actually the oldest part of the city, where the rulers of the early Polish state in the 10th century had one of their palaces.