The central role of the human population of any sociopolitical unit has long been recognized by historians: the number of people, along with such variables as rates of fertility and mortality, help to determine certain economic processes and social policies, and are in turn influenced by other variables such as the efficacy of medical practices and the incidence of warfare. Even when census-derived head counts become available in the early nineteenth century, the precise nature and significance of population movements are not easy to evaluate. These preliminary remarks underline the one stark, unalterable fact about the population of medieval Ireland: there is no evidence on which to base a scientifically respectable figure. Nevertheless two numerical counts, one for the early Middle Ages and one for the late Middle Ages, more certainly in the future and more tentatively here provide grounds for arguments by which generally agreed estimates might be attained.
The Early Middle Ages
The first numerical count is of over forty-five thousand ringforts—earthen raths and stone-built cashels to defend against cattle raids—in the period centered on the seventh to ninth centuries. Crucial to this argument is that these enclosed farmsteads were the dominant settlement form and that they were built and occupied contemporaneously. These were the homes of the great majority of lords and farmers (divided by brehon lawyers into numerous subcategories). A generous multiplier of ten to allow for dependent relatives and servile personnel would produce a base figure of 450,000. In addition there were at least two larger settlement forms: the secular dun, many of which may no longer have served as permanent residential complexes, and ecclesiastical sites. The latter, often visible in the modern landscape as ovoid enclosures, numbered several hundred. To judge by the well-known description of Kildare in circa 630 by Cogitosus in his Vita Brigitae, the greatest monasteries were populous places, with outer zones (here called "suburbs") that provided accommodation for resident craftwork-ers and visiting pilgrims. On this basis a minimum figure of half a million inhabitants would be a reasonable estimate.
Whatever "guestimate" is favored, the population of early medieval Ireland was not stable but, on the contrary, was subject to both upward and downward pressures. The wealth of Roman Britain had attracted Irish as well as Germanic raiders and settlers. In the late fourth and the fifth century there was migration from Ireland to western parts of Britain: to Dyfed and Gwynedd in Wales and to Cornwall in England. The best indication of the scale and scope of this migration is the distribution of ogam inscriptions, which are concentrated in southwest Wales and which suggest that the majority of migrants came from Munster and Leinster. At the opposite end of the island an ultimately more significant migration of the Ulaid to southwestern
Scotland began around 500 c.e. when the royal family of Dal Riata, under Fergus son of Erc, abandoned Dunseverick and resettled across the North Channel. This population movement took on a well-known religious dimension with the settlement of Colum Cille and his followers on Iona in 563. Like Colum Cille’s mission, these migrations may have been purely opportunistic; they may on the other hand be indicative of localized overpopulation in parts of Ireland.
Then came the first historically recorded plague pandemic of the mid-sixth century, whose demographic consequences cannot be measured scientifically but which may have been severe. The introduction of the mouldboard plough around 600 c.e. is believed by some scholars to have led to dietary improvements and to a steady growth of population, coinciding with the great age of ringfort and monastic construction. The introduction of water mills and legal texts dealing with mill construction, milling, and the status of millwrights point in the same direction. The subsequent influx of Scandinavian settlers (Vikings) in the ninth and tenth centuries was probably limited, to judge by the lack of rural placenames when compared with those of England, Scotland, and Normandy. Most of the newcomers would have been males from Norway or from Norwegian colonies in western Scotland; their influence is likely to have been cultural rather than numerical.
The Late Middle Ages
The second numerical count is that of parishes, of which there were about twenty-four hundred. Medieval parishes varied enormously in size: at one extreme were the extensive parishes of the most mountainous districts; at the other the smallest parishes of inner Dublin amounting to a few acres of ground, though with a population of several hundred. In the year 1300 Dublin had sixteen parish churches, seven within the walls and nine outside. If the estimated total population of the city at that time of eleven thousand can be accepted, the average number of parishioners per parish would have been a little under seven hundred. This sort of calculation gives some indication of maximum density of inhabitants, but until a wide range of local studies of medieval parishes and their population has been undertaken, we cannot go beyond mere guesswork. Thus, for example, average densities across the whole island of three to four hundred parishioners yield crude minimum and maximum totals of 720,000 and 960,000. Since it is generally supposed that in the great age of population growth in the twelfth and thirteenth centuries the number of inhabitants doubled or even trebled, the higher of these estimates is probably nearer the mark. One critical factor here is the comparatively low level of urbanization in medieval Ireland, where only about one-fifth of the island would have had regular access to town life even at the height of the Anglo-Norman colony around 1270. Accordingly the population increase experienced in Ireland is unlikely to have matched that achieved in more urbanized parts of Britain and the Continent.
In the late Middle Ages the great demographic enforcer was the second recorded plague pandemic commonly known as the Black Death, which first struck the country in 1348. Before then, there was significant immigration into Ireland, mainly from England and Wales, of people who congregated on rural manors and in towns. In addition aristocratic households established themselves in castles. The size of this influx of "new foreigners" is unknown, but their administrative and cultural impact is likely to have far outweighed their numerical strength. Epidemiological observations based on modern incidences of plague, together with a small amount of contemporary evidence, suggest that the colonists (as distinct from the natives) may have suffered a 40 percent reduction of population through a combination of mortality and emigration. An inquisition at Youghal, for instance, implies a mortality rate of around 45 percent in the case of burgess households. To all appearances and for a variety of reasons, the Gaelic Irish experienced lower death rates and indeed some of them migrated to the towns, including Dublin. Large herds of livestock (Irish caoraigheacht) are a manifestation of widespread internal migration from the late fourteenth century onwards. The demographic low may have reached the half million mark and the country remained underpopulated during the sixteenth century.
