Protohistory of Ireland
The prehistory of Ireland included a protohistorical period, when the literate cultures of Greece and Rome began to take notice of it, and a further proto-literate period of ogham epigraphy, before the early historical period began in the 5th century. Attempts have been made to reconstruct the political developments of this period by reference to early medieval Irish genealogical texts. Ireland in Classical literature. Early references. Classical writers occasionally refer to Ireland under a variety of names, but these references contain little reliable information. For example, Diodorus Siculus claims that the "Prettanoi" of the island of  Iris eat human flesh. Strabo, who calls the island "Ierne", repeats the accusation, adding that they consider it honourable to eat their dead fathers, and openly have sex with their mothers and sisters (although he is sceptical about his sources). Pomponius Mela calls it "Iuverna" and says that, although the climate is unfavourable for grain, grass grows so richly that cattle burst if unrestrained from eating it. Julius Caesar, in his "Commentarii de Bello Gallico", is the first to call the island "Hibernia", describes it as about half the size of Britain, and correctly places it to the west of  Britain – unlike Strabo, who places it to the north. Tacitus. Tacitus says that his father-in-law Gnaeus Julius Agricola, while governor of Britain (AD 78–85), considered conquering Ireland, believing it could be held with one legion plus auxiliaries, and entertained an exiled Irish petty king with the intention of making him the pretext for conquest. Parallels have been drawn with the Irish legend of Túathal Techtmar, who is said to have been exiled to Britain as a child and returned with an army to claim the kingship of Tara in the 1st century. Tacitus also says that most of  the harbours and approaches to Ireland were known through commerce, but inaccurately locates the island between Britain and the Iberian peninsula. Juvenal. The 2nd-century poet Juvenal, in his second "Satire", contrasting the victories of the Roman army with the low morals of the people at home in Rome, says that, as well as conquering Britain and the Orkney islands, "we have advanced arms beyond the shores of "Iuverna"". Although Juvenal is not writing history, it is possible that he is referring to a genuine Roman military expedition to Ireland. Ptolemy. The 2nd-century Alexandrian Greek writer Ptolemy, one of  the most important geographers, mathematicians and astronomers in the ancient world, refers to Ireland in two of his works. In the astronomical treatise known as the "Almagest" he gives the latitudes of an island he calls "Mikra Brettania" (Μικρὰ Βρεττανία) or "Little Britain" (the south of the island at 58 degrees, the north at 61 degrees). In his "Geography", at the same latitudes, he places the Prettanic island "Iwernia", next to its neighbour, the Prettanic island "Albion" (Great Britain). The "Geography" contains the most detailed account of Ireland in classical literature, giving the latitude and longitude of six promontories, fifteen  river mouths, ten settlements and nine islands, and naming sixteen population groups. North coast. Ptolemy describes the northern coast of Ireland, from the Northern Promontory (possibly Bloody Foreland or Rossan Point in County Donegal) in the west, to the "Wenniknion" promontory (probably Malin Head), the mouth of the river "Widwa" (probably the Foyle), the mouth of the river "Argita" (perhaps the Bann) and the "Rhobogdion" promontory (Fair Head, County Antrim) in the east. The peoples who inhabit the north coast are the "Wenniknioi" in the west and the "Rhobogdioi" in the east. West coast. The west coast is poorly represented  compared to the other three, and identification of the names Ptolemy gives is speculative. He begins with the Northern Promontory (see above), and working north to south names the river "Rhawiu" (possibly the Erne); the town "Magnata" (a settlement of the "Magnatai" people, possibly somewhere in County Sligo); the mouth of the rivers "Libniu" (possibly Clew Bay), "Ausoba" (perhaps Galway Bay) "Senu" (probably the Shannon, although placed too far to the north), "Dur" (possibly Dingle Bay) and "Iernu" (possibly the Kenmare), and the Southern Promontory (any one of Slea Head, Bray Head, Dursey Head and Mizen Head). Peoples of this  coast are: the "Erdinoi" near Donegal Bay; the "Magnatai" or "Nagnatai" of County Mayo and Sligo; the "Auteinoi" between County Galway and the Shannon, identifiable with the early medieval Uaithni; the "Ganganoi", also known in north Wales, and the "Wellaboroi" in the far south-west. South coast. The south coast stretches from the Southern Promontory to the mouths of the rivers "Dabrona" (possibly the Lee or the Blackwater) and "Birgu" (probably the Barrow) and the Sacred Promontory (Carnsore Point, County Wexford). Peoples of the south coast are the "Iwernoi" in the west, who share their name with the island, "Iwernia , and can be identified with the early medieval Érainn; the Usdiai", and the "Brigantes" in the east, who share their name with a people of Roman Britain. East coast. From the Sacred Promontory in the south to the "Rhobogdion" promontory in the north, Ptolemy names the river "Modonnu" (possibly the Slaney, but more likely the Avoca), the town of "Manapia" (a settlement of the "Manapii"), the river "Oboka" (perhaps the Liffey; the river Avoca takes its modern name from a misinterpretation of Ptolemy's "Oboka"), the town of "Eblana" (a settlement of the "Eblanoi", formerly mistakenly identified with Dublin), the  river "Buwinda" (the Boyne), the promontory "Isamnion", the river "Winderios" (possibly Carlingford Lough, Dundrum Bay or Strangford Lough), and the river "Logia" (Belfast Lough, "Loch Laoigh" in Irish). Peoples named, from south to north, are: the "Koriondoi"; the "Manapioi", possibly related to the Menapii of Gaul; the "Kaukoi", probably not related to the Germanic Chauci of the Low Countries; the "Eblanoi"; the "Woluntioi", identifiable with the early medieval Ulaid; and the "Darinoi". Later references. Roman sources mention raids on Britain by Saxons of north-west Germany, by Picts from Scotland and by two groups of people usually associated with Ireland , the Scotti and the Atacotti. The origins and meanings of Scotti and Atacotti is uncertain. Atacotti disappears with the Romans. Scotti means Gaels to Adomnán in the late seventh century, but not to Columbanus in the early sixth century, who uses the older term Iberi instead. The Scotti are perhaps a confederation of tribes in Ulster, and the Atacotti one in Leinster, but this is not certain.