Defining religio romana

What I practise, I broadly categorise as a form of Roman Reconstructionist devotional polytheism.

But what is Roman Reconstructionism? What demarcates it as 'Roman' as opposed to other ancient cultures? Why reconstruct? From where did it originate?

In its current form, the Roman Reconstructionist religion can be traced to the general wave of reconstruction-oriented Paganism that came to a head in the 1990s. Greek reconstructionists had a fair amount of success in getting their message out, and Celtic reconstructionism developed as a legitimate alternative to Neodruidry in the 1980s. Those who were oriented more towards Roman culture, gods, and history also sought this success in developing a recognisable religious tradition. To this end, certain groups were organised, the most prominent and largest amongst them being Nova Roma. A variety of issues sprang up and the group has gone into a long decline over the years, but it once was a large and active community of Roman reconstructionists--with significant contributions from the historical reenactor crowd and others who were simply interested in emulating Roman values and culture. But the religious aspect of it never went away entirely, and inspired a host of other groups to form up with a stronger focus on the religion. And it left behind an extensive network of mailing lists, digital temples, and discussion boards. And for now, that's as far as I'm touching that messy subject.

This religious movement is also referred to in Latin as Religio Romana (Roman religion) and Cultus deorum romanorum (cult to the Roman gods). This leads into what delineates it; put simply, it focuses on historical Roman methods of worship, religious customs, folklore, and theology--especially of traditions prior to the deep Hellenisation of the Late Republic. Now, because Roman historical religion was uniquely syncretistic, modern Roman revival religion tends to be more tolerant of individual cults to non-Roman gods, and syncretism between cults within a broad Roman framework. But the primary focus is on the ancestral religious customs of Roman culture and society.

Why reconstruct? This is actually a very valid question. Historical Roman society and culture had a great deal of ugliness. Its values sometimes seem strange to us, and not always were they particularly inspiring. Misogyny, violence, slavery, rape, and domination were regular parts of Roman culture. The roots of toxic ideas of cultural masculinity can be found in Roman virtues of manliness. Why would we want to reconstruct that?
The answer is complex. On one hand the simple truth is, we don't. We don't want to revive those ugly cultural values, where people were treated as property and social class determined your legal rights. But we do want to revive the virtues and values of the Romans--and their affiliate ethnic groups and peoples--that were admirable to our modern eyes. Accommodations to modernity are made as little as possible, when it comes to religious practices. But when it comes to modern ethics of human rights, human dignity, and respect, I don't believe anyone seeks to bring back Roman chauvinism.
The reconstructionism is aimed at two main goals: to revive the honourable and admirable elements of Roman culture, and to revive as best we can the religious, spiritual, and folkloric customs of ancient Roman people. Why people do the latter is a question of many answers, each different from person to person; but I think a general trend can be drawn in regards to Reconstructionism and devotional Polytheism as a whole. It is that reconstructionists seek to honour certain deities whose identities are so tied to a specific culture, and they feel that it is most respectful to honour them in a manner what would be recognisable to that culture.