Ostrów Tumski ("Cathedral Island", German: Dominsel) is the oldest part of the city of Wroc aw in south-western Poland. It was formerly an island (ostrów in old Polish) between branches of the Oder River. Archaeological excavations have shown that the western part of Ostrów Tumski, between the Church of St. Martin and the Holy Cross, was the first to be inhabited. The first, wooden church (St. Martin), dating from the 9th century, was surrounded by defensive walls built on the banks of the river. The island had approximately 1,500 inhabitants at that time. The first constructions on Ostrów Tumski were built in the 10th century by the Piast dynasty, and were made from wood. The first building from solid material was St. Martin's chapel, built probably at the beginning of the eleventh century by Benedictine monks. Not long after the first cathedral was raised, in place of the small church.