In the later Western Roman Empire, following the reorganization of Diocletian, a pagus (compare French pays, Spanish pago, "a region, terroir") became the smallest administrative district of a province. By that time the word had long been in use with various meanings. Smith's Dictionary says of it, "The meaning of this word cannot be given in precise and absolute terms, partly because we can have no doubt that its significance varied greatly between the earliest and the later times of Roman history, partly because its application by Latin writers to similar, but not identical, communities outside Italy ..."
Pāgus is a native Latin word from a root pāg-, a lengthened grade of Indo-European *pag-, a verbal root, "fasten" (English peg), which in the word may be translated as "boundary staked out on the ground." In semantics, *pag- used in pāgus is a stative verb with an unmarked lexical aspect of state resulting from completed action: "it is having been staked out," converted into a noun by -us, a type recognizable in English adjectives such as surveyed, defined, noted, etc. English does not use the noun: "the surveyed," but Latin characteristically does. Considering that the ancients marked out municipal districts with boundary stones, the root meaning is nothing more than land surveyed for a municipality with stakes and later marked by boundary stones, a process that has not changed over the millennia.
Earlier hypotheses concerning the derivation of pāgus suggested that it is a Greek loan from either πήγη, "village well," or πάγος, "hill-fort." William Smith opposed these on the grounds that neither the well nor the hill-fort appear in the meaning of pāgus.
Roman usage 
The pagus and vicus (a small nucleated settlement or village) are characteristic of pre-urban organization of the countryside. In Latin epigraphy of the Republican era, pagus refers to local territorial divisions of the peoples of the central Appennines and is assumed to express local social structures as they existed variously.
As an informal designation for a rural district, pagus was a flexible term to encompass the cultural horizons of "folk" whose lives were circumscribed by their locality: agricultural workers, peasants, slaves. Within the reduced area of Diocletian's subdivided provinces, the pagi could have several kinds of focal centers. Some were administered from a city, possibly the seat of a bishop; other pagi were administered from a vicus that might be no more than a cluster of houses and an informal market; yet other pagi in the areas of the great agricultural estates (latifundia) were administered through the villa at the center.
The historian of Christianity Peter Brown has pointed out that in its original sense paganus meant a civilian or commoner, one who was excluded from power and thus regarded as of lesser account; away from the administrative center, whether that was the seat of a bishop, a walled town or merely a fortified village, such inhabitants of the outlying districts, the pagi, tended to cling to the old ways and gave their name to "pagans"; the word was used pejoratively by Christians in the Latin West to demean those who declined to convert from the traditional religions of antiquity.
Post-Roman pagus 
The pagus survived the collapse of the Empire of the West, retained to designate the territory controlled by a Merovingian or Carolingian count (comes). Within its boundaries, the smaller subdivision of the pagus was the manor. The majority of modern French pays are roughly coextensive with the old counties (e.g., county of Comminges, county of Ponthieu, etc.) To take an instance, at the beginning of the 5th century, when the Notitia provinciarum was drawn up, the Provincia Gallia Lugdunensis Secunda formed the ecclesiastical province of Rouen, with six suffragan sees; it contained seven cities (civitates). For civil purposes, the province was divided into a number of pagi: the civitas of Rotomagus (Rouen) formed the pagus Rotomagensis (Roumois); in addition there were the pagi Caletus (Pays de Caux), Vilcassinus (the Vexin), the Tellaus (Talou); Bayeux, the pagus Bajocassinus (Bessin), and the Otlinga Saxonia; that of Lisieux the pagus Lexovinus (Lieuvin); that of Coutances the p. Corilensis and p. Constantinus (Cotentin); that of Avranches the p. Abrincatinus (Avranchin); that of Sez the p. Oximensis (Hiémois), the p. Sagensis and p. Corbonensis (Corbonnais); and that of Evreux the p. Ebroicinus (Evrecin) and p. Madriacensis (pays de Madrie) (EB "Normandy").
The pagus was the equivalent of what English-speaking historians sometimes refer to as the "Carolingian shire", which in German is the Gau. In Latin texts, a canton of the Helvetic Confederacy is rendered pagus.
- Smith, William; Wayte, William; Marindin, George Eden (1891). "Pagus". A Dictionary of Greek and Roman Antiquities. Volume 2 (Third ed.). London: John Murray. pp. 309–311.
- Watkins, Calvert (1992). Indo-European Roots. "pag-". The American Heritage Dictionary of the English Language (Third ed.). Boston: Houghton Mifflin Company.
- Oxford Latin Dictionary (Oxford: Clarendon Press 1982, 1985 printing), entry on pagus, p. 1283.
- Commentarii de Bello Gallico 1.12.4: nam omnis civitas Helvetia in quattuor pagos divisa est ("for the Helvetian nation as a whole was divided into four cantons"). Pagus in this sense is sometimes translated "tribe"; the choice of "canton" may be influenced by later usage of the word in regard to Helvetia.
- Guy Jolyon Bradley, Ancient Umbria: State, Culture, and Identity in Central Italy from the Iron Age to the Augustan Era (Oxford University Press, 2000), p. 56 online.
- Peter Brown, entry on "Pagan," Late Antiquity: A Guide to the Postclassical World, edited by G.W. Bowersock, Peter Brown, and Oleg Grabar (Harvard University Press, 1999), p. 625 online: "The adoption of paganus by Latin Christians as an all-embracing, pejorative term for polytheists represents an unforeseen and singularly long-lasting victory, within a religious group, of a word of Latin slang originally devoid of religious meaning. The evolution occurred only in the Latin west, and in connection with the Latin church. Elsewhere, 'Hellene' or 'gentile' (ethnikos) remained the word for 'pagan'; and paganos continued as a purely secular term, with overtones of the inferior and the commonplace."