Dodd's slope was was opened in 1840 by the Blaenavon Ironworks Company. It was later superseded by Big Pit, where the shaft was sunk in 1860 and deepened c 1880. Big Pit was operated in connection with Blaenavon Ironworks Company, then by the National Coal Board from 1947 to 1980.

The drift entrance comprises a late C19 semi-circular arch with an inner order of white brick and an outer order of red brick. The steeply inclined entrance has brick retaining walls.

R Hayman, Hayman & Horton, 30/12/2002