In 1547 iron smelting was being carried out at Mwynddu by William Herbert. He had received charters granted by Henry VIII and Edward VI. Originally the mines were possibly open cast and drift workings in the vicinity of Mwyndy House, roughly where the modern Mwyndy industrial estate and ponds are now.
They were known as Mwynddu pits.
The pits were also extensively worked as quarries in the 18th and 19th centuries.
This may have destroyed earlier workings, suggested in 1903 to be of Roman date of which there is now no trace. The pits, situated immediately north-west and north-east of the house, had been filled in or become waterlogged by 1956.
Wooden shovels of Roman origin were said to have been found in old workings. Also there is a massive wall along the road to Groes Faen reputed to be Roman.
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