Complex sentence: From the late 18th century numerous large-scale industrialised collieries operated in the southern section of the North East Wales coalfield, alongside hundreds of more traditional small-scale pits belonging to a mining tradition dating back to the Middle Ages.
Split into simpler sentences: From the late 18th century numerous large-scale industrialised collieries began to capitalise on the location of the area on the southern section of the North East Wales coalfield. These collieries operated in the area alongside hundreds of more traditional small-scale pits belonging to a mining tradition dating back to the Middle Ages.