Vincent of Lérins was a 5th-century Gallic monk and presbyter born in Toulouse. After an early life involving secular pursuits, he joined the monastery on the Lérins Islands. He is most famous for composing the *Commonitorium* around 434, a text intended to help distinguish orthodox Christian belief from heresy. Throughout his life, he defended traditional doctrines, such as the title of Mary as *Theotokos*, and his writings continue to influence discussions regarding the development of Christian dogma.