 Saint Columba then began the conversion of the Dál Riata and the other peoples of Scotland, although native saints such as Mungo also arose.The history of Christianity in Cornwall is more obscure, but the native church seems to have been greatly strengthened by Welsh and Irish missionaries such as Saints Petroc, Piran, and Breaca.Extreme weather (as around 535) and the attendant famines and disease, particularly the arrival of the Plague of Justinian in Wales around 547 and Ireland around 548, may have contributed to these missionary efforts.