The Commonitorium or Commonitory is a 5th-century Christian treatise written after the council of Ephesus under the pseudonym “Peregrinus” and attributed to Vincent of Lérins.[2][3] It is known for Vincent’s famous maxim: “Moreover, in the Catholic Church itself, all possible care must be taken, that we hold that faith which has been believed everywhere, always, by all.”[3](p132)[a]