Kuyavian Pyramids, known as Kuyavian Mounds, Graves of Giants or Polish Pyramids are enormous tombs, megalithic structures in Kuyavia, Poland. They were built in the late stages of the Younger Stone Age, over a period of no more than 500 years. They demonstrate a relatively high level of architectural knowledge, the ability to use simple devices such as levers, and good organization of their builders' work. The orientation of the graves relative to the cardinal directions (east-west) indicates knowledge of certain basic astronomy.