 The Franciscans used a method of mass conversion, sometimes baptizing many thousands of Indians in a day.This method was championed by prominent Franciscans such as Toribio de Benavente, known as "Motolinia", and Las Casas made many enemies among the Franciscans for arguing that conversions made without adequate understanding were invalid.Las Casas wrote a treatise called ""De unico vocationis modo"" (On the Only Way of Conversion) based on the missionary principles he had used in Guatemala.