and in the evening, while sacrifices were being offered, but were fasti in the middle of the day. By the late 2nd century AD, extant calendars no longer show days marked with these letters, probably in part as a result of calendar reforms undertaken by Marcus Aurelius. Days were also marked with nundinal letters in cycles of A B C D E F G H, to mark the "market week" (these are omitted on the table below). On a dies religiosus, individuals were not to undertake any new activity, nor do anything other than tend to the most basic necessities. On the calendar under the Republic, 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. 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. 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". Unless otherwise noted, the dating and observances on the following table are from H.H. Scullard, Festivals and Ceremonies of the Roman Republic (Cornell University Press, 1981), pp. 69–84. See also Month names: Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, December. Leap month: Mercedonius or Intercalaris. References Months of the Roman calendar February