Marcos de Niza (märˈkōs dā nēˈsä) [key], c.1495–1558, missionary explorer in Spanish North America. A Franciscan friar, he served in Peru and Guatemala before going to Mexico. There he headed an expedition (1539) planned by Antonio de Mendoza, who had been excited by Cabeza de Vaca's stories of rich Native American pueblos. Fray Marcos traveled north at least into SE Arizona and perhaps into New Mexico. Probably duped by Zuñi legends, the friar described with enthusiasm and great inaccuracy the fabulous riches of the Seven Cities of Cibola. They proved to be only fables when Francisco Vásquez de Coronado led (1540) his soldiers there. Fray Marcos was dismissed as guide and sent back in disgrace.