 There he dedicated himself to the study of the indigenous languages and became proficient in Otomi and then in Nahuatl.He was a friend of the Bishop and later Viceroy of New Spain, Juan de Palafox y Mendoza, as is documented by surviving letters written by Carochi to the bishop.Carochi had an acute understanding of the Nahuatl language and was the first grammarian to understand and propose a consistent transcription of two difficult phenomena in Nahuatl phonology, namely vowel length and the saltillo.