Because of its relative isolation from other Spanish-speaking areas over most of its 400-year existence, New Mexico Spanish, and in particular the Spanish of northern New Mexico and Colorado has retained many elements of 16th- and 17th-century Spanish and has developed its own vocabulary. In addition, it contains many words from Nahuatl, the language spoken by the ancient Aztecs of Mexico. New Mexican Spanish also contains loan words from the Pueblo languages of the upper Rio Grande Valley, Mexican-Spanish words (mexicanismos), and borrowings from English. Grammatical changes include the loss of the second person verb form, changes in verb endings, particularly in the preterite, and partial merging of the second and third conjugations.