As for the place, Hesiod asserts that a bronze anvil falling from heaven would fall nine days before it reached the earth. The anvil would take nine more days to fall from earth to Tartarus.[5] In the Iliad (c. 700 BC), Zeus asserts that Tartarus is “as far beneath Hades as heaven is above earth.”[6] Similarly the mythographer Apollodorus, describes Tartarus as “a gloomy place in Hades as far distant from earth as earth is distant from the sky.”[7]

Source: Tartarus – Wikipedia