 The earliest known religious monument is the Catholic holy well in Penrhys first mentioned in the 15th century , though it may have been a place of pagan worship before this . This pilgrimage site was identified as a ' manor ' belonging to the Cistercian Abbey of Llantarnam and was seen as one of the most important religious sites in Wales , because of its Marian shrine . This holy site was the main reason people would pass through the commote ; it was even thought to be the main reason why the first bridges were built over the River Rhondda . 
