Llandeilo is named after one of the better known Celtic saints of the 6th century, Saint Teilo. The Welsh word 'llan' signified a religious enclosure, normally one dedicated to a particular saint (this corresponds, today, to 'church of'). Saint Teilo, who was a contemporary of Saint David the patron Saint of Wales, established a small monastic settlement or 'clas' on the site of the present-day church. Although there is very little factual detail about the life of Saint Teilo, the fact that he was highly respected in his lifetime and revered after his death is shown by the forty-five places dedicated to him, some as far afield as Brittany. Source: Wikipedia