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The main catalyst for its transformation from a small town into a big city was the demand for coal required in making iron and later steel , brought to the sea by packhorse from Merthyr Tydfil .
 Merthyr Tydfil
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Merthyr Tydfil