Nonius Marcellus was a Roman grammarian and lexicographer who lived during the late 1st century BC and early 1st century AD. He is best known for his work titled "De Compendiosa Doctrina," which focused on the study of language and grammar. His contributions helped preserve and clarify the Latin language during a time of significant linguistic change. In addition to his grammatical work, Nonius Marcellus compiled a dictionary of rare and obscure words, providing valuable insights into the vocabulary of his time. His writings are often referenced by later scholars, including Isidore of Seville and Varro, highlighting his influence on the study of language in ancient Rome.