A number of Neolithic cultures recognized near the Amur River in eastern Siberia. They are mainly defined by the presence of pottery. In the Middle Amur region, the earliest phase is known as the Novopetrovka blade culture. Later is the Gromatukha culture, with unifacially flaked adzes, bifacially flaked arrowheads, and laurel-leaf knives and spearheads. Settlements on Osinovoe Lake, which are characterized by large pit houses, date to around the 3rd millennium BC. Millet was cultivated, representing the first food production in the area, and there was fishing. A fourth Neolithic culture in the area, dating to the mid-2nd millennium BC was a combination of farming and fishing by people who moved there from the Lower Amur area. The Neolithic of the Lower Amur is known from sites such as Kondon, Suchu Island, and Voznesenovka. Fishing provided the economic basis for the establishment of unusually large sedentary settlements of pit houses - a situation paralleling the examples from the Northwest coast of North America. In the 1st millennium BC, iron was introduced and fortified villages constructed. In Middle Amur, millet farming became the lifeway.