Netherlands, megalithic structures can be found in the northeast of the country, mostly in the province of Drenthe. Knowth is a passage grave of the Brú na Bóinne neolithic complex in Ireland, dating from c. 3500–3000 BC. It contains more than a third of the total number of examples of megalithic art in all Europe, with over 200 decorated stones found during excavations. African megaliths North Africa Nabta Playa at the southwest corner of the western Egyptian desert was once a large lake in the Nubian Desert, located 500 miles south of modern-day Cairo. By the 5th millennium BC, the peoples in Nabta Playa had fashioned an astronomical device that accurately marks the summer solstice. Findings indicate that the region was occupied only seasonally, likely only in the summer when the local lake filled with water for grazing cattle. There are other megalithic stone circles in the southwestern desert. At Nabta Playa, located in Egypt and broader region of the Eastern Sahara, there is a megalithic cultural complex (e.g., sacrificed cow burial site, solar calendar, altar) that dates between 4000 BCE and 2000 BCE. Likely part of Copper Age and Bronze Age cultural traditions of megalith-building, megaliths (e.g., dolmens) were constructed in Mediterranean North Africa. West Africa In Cross-River State, Nigeria, there are megalithic monoliths of an anthropomorphic nature. At Tondidarou, in the Malian Lakes Region, there are megaliths of an anthropomorphic nature (e.g., face, navel, scarifications) that date between 600 CE and 700 CE. Between 1350 BCE and 1500/1600 CE, Senegambian megaliths (e.g., tumuli) were constructed for the purpose of ancestral reverence. Central Africa In the northwestern region of the Central African Republic, there are megaliths that were created for various purposes (e.g., burial, ritual performances). Between late 3rd millennium BCE and mid-2nd millennium CE, megaliths (e.g., monuments, cairn burials) were constructed in the regions (e.g., Eastern Adamawa, Oubanguian Ridge, Chad/Congo watershed) in Central African Republic and Cameroon, throughout various periods (e.g., Balimbé: 2000 BCE – 1000 BCE; Early Gbabiri: 950 BCE – 200 BCE; Late Gbabiri: 200 BCE – 500 CE; Bouboun: 500 CE – 1600 CE), for various purposes (e.g., ritual practices, territorial marking). Eastern Africa In the Ethiopian Highlands of Harar, the earliest construction of megaliths occurred. From this region and its megalith-building tradition (e.g., dolmens, tumuli with burial chambers organized in cemeteries), the subsequent traditions in other areas of Ethiopia likely developed. In the late