The Neolithic barrow grave at Kruszyn discovered in 2009, dates back to the first half of the third millennium BC. It beloengs to a small regional group of the Corded Ware culture.
See:
Łukasz Pospieszny et all., Remains of a late Neolithic barrow at Kruszyn. A glimpse of ritual and everyday life in early Corded Ware societies of the Polish Lowland, in: Praehistorische Zeitschrift Vol 90,(1-2), 2015 , pp. 185-213