Grimes Graves are neolithic flint mines near Thetford, Norfolk, the only flint mines in UK open to the public. The Anglo-Saxons named them Grimes Graves, but it was not until Victorian times that they were excavated and it was discovered that they were nearly 5,000 years old. Over 400 pits were dug here, but only one is open to the public. Miners sought much prized black flint for use in tools weapons, ceremonial items etc. For further information see; https://www.english-heritage.org.uk/visit/places/grimes-graves-prehistoric-flint-mine/history/.