Salvete
The distinction between Quirinus and Mars traces back to when the Septimontium was composed of communities still identifiable as seperate. It is probably not correct to think the Palatine entirely Latin and the Quirinal as entirely Sabine, as such communities were usually of a mixed ethnicity. But the antiquarians of the Late Republic, notably Varro, identified an original Quirinus as Sabine, primarily because His temple was on on the Quirinal that tradition held to be first settled by Tatius. We know that there was a second aurguralium on the Quirinal, suggesting again when there were two separate cities in the area. The one on the Arx used by Roman augurs was set at the house of Tatius, apparently after he took the citidal in his war with the Palatines. And there was a separate group of Salii of the Quirinal, maybe associated with Quirinus, maybe with Mars as was the Palatine Salii. Maybe the Quirinal Salii performed at the time of the Quirinalia. Maybe, we just don't know anything more about the Quirinal Salii other than they existed.

In the fourth century Quirinus became identified with Romulus, and most of what we know of Quirinus comes from the later period when His myth is reworked to fit into the imperial ideology. About the same time there is a new Latin mythos identifying their origin with Aeneas. This apparently began at Lavinium, taken over by Rome after 388, and then the tumulus identified with Aeneas was built around 304 just after the extramural Latin shrine was completely rebuilt. Major changes to the Religio Romana in this period are comparable to that of the Augustan Restoration, so we have lost whatever roots there were to Quirinus originally.

Both Quirinus and Mars were war gods. Their role as agricultural gods is really about Their defending communities and their crops against disease. The rite of the Salii, for example, is not a preparation for the season of war, as some historians have posed. Instead it is a rite to rid the city of disease when spring fevers were prevelent. Quirinus shows up in some rites only through the participation of the flamen Quirinalis. At Robigalia the flamen may be acting in place of an earlier version of the war god Quirinus. And there again it is meant for Quirinus to drive off disease, rust on crops. In the other rites though, the flamen Quirinalis appears primarily as a stand in for Romulus. For example the parentalia he performed at the tomb of Acca Laurentina in December. In some ways Mars and Quirinus took on two aspects of a warrior society such as Rome had in the Early Republic. Mars is the fierce warrior in time of war, Quirinus is more like Romulus, the veteran warrior always on guard while in the time of peace. The Romans refered to themselves as Quirites when in assembly with this idea that although at peace, and thus able to assemble in comitia, they were still well prepared to defend the city. That idea is also behind the invocation that called Janus Quirinus, or the warrior/guardian of the gates Janus in a time of relative peace. Other notions of Quirinus being solely a third function agricultural deity is based in erroneous preconceptions that has no resemblence to Roman social structure. Quirinus appears only as a warrior deity or as a form of Romulus.