The title is a reference to Pax Romana, the long period of relative peace in the Roman Empire from the beginning of Augustus Caesar's reign in 27 B.C. to the end of Marcus Aurelius' in 180 A.D. (And Livia Soprano, fittingly or ironically, shares the same first name as Emperor Augusta's wife and trusted advisor, Livia.)
The waterfall seen in this episode is The Great Falls of the Passaic River, located in Paterson, New Jersey.
The song played over the ending credits is "Paparazzi" by Xzibit.
The quote about the father and the son up on the hill and the cows was also said in the movie Colors (1988).