The Calenar of saints is a traditional Christian method of organizing a liturgical year on the level of days by associating each day with one or more saints, and referring to the day as that saint's feast day. The system arose from the very early Christian custom of annual commemoration of martyrs on the dates of their deaths, or birth into heaven (and thus referred to in Latin as dies natalis, "day of birth"). As the number of recognized saints increased during Late Antiquity and roughly the first half of the Middle Ages, eventually every day of the year had at least one saint who was commemorated on that date. Eventually, some saints were moved to another day in some traditions, or completely removed; thus, some saints do have more than one day.