King coal tells castle story.
The piece of coal, hewn from the seams at Lewis Merthyr Colliery, Trehafod, has been put on display at Cardiff Castle's interpretation centre. Nigel Howells, Cardiff council's cabinet member for culture, said the coal was there to show visitors what was behind the wealth and opulence of the castle.
He said: "The success and wealth of Cardiff owes a great deal to the hard work of everyone involved in the coal industry of South Wales, particularly in the Rhondda Valleys. We want visitors who come to the castle and see the opulent interiors to know that the contribution is valued and recognised.
To capitalise on the links between Cardiff and the collieries, Cardiff Castle and the Rhondda Heritage Park have begun a joint marketing initiative which will go live in February 2011."
The initiative, dubbed Heritage Afloat Wales, was launched last month.
Historian John Davies said the boom of the coal industry in South Wales had transformed Cardiff into the biggest coal-exporting port in the world.