Medieval legend made him responsible for the conversion of emperor Constantine. Among the Western churches, the feast day is held on the anniversary of Saint Sylvester's death, 31 December, a date that, since the adoption of the Gregorian calendar, has coincided with New Year's Eve.
Medieval legend positioned him as the catalyst for Emperor Constantine's conversion. In Western Christian communities, his feast day is celebrated on the anniversary of Saint Sylvester's passing, December 31, a date that has coincided with New Year's Eve since the introduction of the Gregorian calendar.