The erudite Roman Varro (116-29 B.C.) says the name of Rome was once Septimontium. This would have been before the people living on or around the 7 (septem) hills (montes) called their city Rome. This is also the name of a December 11 festival which included a walk around the hills. In A Topographical Dictionary of Ancient Rome (London: Oxford University Press, 1929), Samuel Ball Platner says Roman antiquarians believed the festival was based on the inclusion within the Roman city limits of the seven hills. There is debate over which hills were included.
"This day in ancient history" caveat: please see Unreliability of Dates.