Mungo was brought up by Saint Serf who was ministering to the Picts in that area. It was Serf who gave him his popular pet-name. At the age of twenty-five, Mungo began his missionary labours on the Clyde, on the site of modern Glasgow. He built his church across the water from an extinct volcano, next to the Molendinar Burn, where the present medieval cathedral now stands. For some thirteen years, he laboured in the district, living a most austere life in a small cell and making many converts by his holy example and his preaching.