A "dies natalis" was an anniversary such as a temple founding or rededication, sometimes thought of as the "birthday" of a deity. During the Imperial period, some of the traditional festivals localized at Rome became less important, and the birthdays and anniversaries of the emperor and his family gained prominence as Roman holidays. On the calendar of military religious observances known as the "Feriale Duranum", sacrifices pertaining to Imperial cult outnumber the older festivals. After the mid-1st century AD, a number of dates are added to calendars for spectacles and games "(circenses)" held in honor of various deities in the venue called a "circus". By the late 2nd century AD, extant calendars no longer show days marked with letters "(F, N, C" and so on) to show their religious status, probably in part as a result of calendar reforms undertaken by Marcus Aurelius. Festivals marked in large letters on extant "fasti", represented by festival names in all capital letters on the table, are thought to have been the most ancient holidays, becoming part of the calendar before 509 BC.