Calendar: It is not essential to follow the traditional religious calendars of ancient Rome for, even when Rome’s empire was at her height, there was no such thing as a universal Roman calendar of religious festivals. Instead, each region of the empire established their own calendar, which did not necessarily mirror the calendar in Rome (Scheid, An Introduction to Roman Religion at 41-42). Furthermore, the religious calendars varied from century to century, so not only were they not uniform from region to region, they were not uniform from century to century either. Add to this the contemporary dilemma of realising that many ancient festivals celebrated the founding of temples that have long since fallen into ruin – if the temple no longer exists then celebrating its coming into being seems somewhat incongruous. And then there is the fact that most Roman oriented polytheists are scattered across the world and are often not in close proximity to each other – making the celebration of ancient festivals feel doubly more incongruous. On top of all this, we note that many ancient celebrations were related to the seasonal cycles of Europe / the northern hemisphere, and thus may not apply to southern hemisphere Pagans, or those living in the tropics.
Nonetheless, learning about the calendars is undoubtedly useful, in terms of understanding how polytheism was practiced in ancient Rome, and observing at least the most important of the festivals may provide a pleasing link between the past and present, as well with other contemporary Roman polytheists – for these reasons many Roman polytheists celebrate Saturnalia at the very least, and may also try to make some kind of observation on certain other days, especially those that are traditionally sacred to patron Gods.