Laudator Temporis Acti

Ramsay MacMullen, The Earliest Romans: A Character Sketch (Ann Arbor: University of Michigan Press, 2011), p. 37, with note on p. 136:

Language itself hints at that Roman ferocity or belligerence, through the word populus in earliest times meaning "infantry" and connected with the verb "to pillage", and this latter right and joy defined the entire community. As to early hostis, it meant a peregrinus, a non-Roman, a foreigner, an enemy, and in the latter sense it came to be standardized. A line called the pomerium ritually drawn around the city set apart two zones of life, as the Romans thought of it: "home" and everything on the far side, "military service".²³ They saw themselves as perpetually an army perpetually at war with absolutely everybody.

23. Populus, cf. Palmer (1974) 6 or Smith (2006) 200; hostis, cf. Watson (1975) 154, in the Twelve Tables, adversus hostem aeterna autoritas [sic, read auctoritas], though perhaps the semantic change peregrinus = hostis dates only to the fourth century, Gargola (1995) 199; and ibid. 26, on the pomerium separating domi and militiae.

The references are to:

• Daniel J. Gargola, Lands, Laws, & Gods: Magistrates & Ceremony in the Regulation of Public Lands in Republican Rome (Chapel Hill: University of North Carolina Press, 1995), not published at "Ithaca NY" as MacMullen indicates on p. 173.
• Robert E.A. Palmer, Roman Religion and Roman Empire: Five Essays (Philadelphia: University of Pennsylvania Press, 1974), not in MacMullen's bibliography.
• C.J. Smith, The Roman Clan: The Gens from Ancient Ideology to Modern Anthropology (Cambridge: Cambridge University Press, 2006)
• Alan Watson, Rome of the XII Tables: Persons and Property (Princeton: Princeton University Press, 1975)

For populus cf. populabundus ("engaged in ravaging a territory") and populor ("ravage, plunder").