Causantín mac Cináeda Causantín or Constantín mac Cináeda ( in Modern Gaelic , " Còiseam mac Choinnich " ; died 877 ) was a king of the Picts . He is often known as Constantine I , in reference to his place in modern lists of kings of Scots , though contemporary sources described Causantín only as a Pictish king . A son of Cináed mac Ailpín ( " Kenneth MacAlpin " ) , he succeeded his uncle Domnall mac Ailpín as Pictish king following the latter ' s death on 13 April 862 . It is likely that Causantín ' s ( Constantine I ) reign witnessed increased activity by Vikings , based in Ireland , in Northumbria and in northern Britain . He died fighting one such invasion . Sources . Very few records of ninth century events in northern Britain survive . The main local source from the period is the " Chronicle of the Kings of Alba " , a list of kings from Cináed mac Ailpín ( died 858 ) to Cináed mac Maíl Coluim ( died 995 ) . The list survives in the Poppleton Manuscript , a thirteenth - century compilation . Originally simply a list of kings with reign lengths , the other details contained in the Poppleton Manuscript version were added from the tenth century onwards . In addition to this , later king lists survive . The earliest genealogical records of the descendants of Cináed mac Ailpín may date from the end of the tenth century , but their value lies more in their context , and the information they provide about the interests of those for whom they were compiled , than in the unreliable claims they contain . The Pictish king - lists originally ended with this Causantín , who was reckoned the seventieth and last king of the Picts . For narrative history the principal sources are the " Anglo - Saxon Chronicle " and the Irish annals . While Scandinavian sagas describe events in 9th century Britain , their value as sources of historical narrative , rather than documents of social history , is disputed . If the sources for north - eastern Britain , the lands of the kingdom of Northumbria and the former Pictland , are limited and late , those for the areas on the Irish Sea and Atlantic coasts — the modern regions of north - west England and all of northern and western Scotland — are non - existent , and archaeology and toponymy are of primary importance . Languages and names . Writing a century before Causantín was born , Bede recorded five languages in Britain . Latin , the common language of the church , Old English , the language of the Angles and Saxons , Irish , spoken on the western coasts of Britain and in Ireland , Brythonic , ancestor of the Welsh language , spoken in large parts of western Britain , and Pictish , spoken in northern Britain . By the ninth century a sixth language , Old Norse , had arrived with the Vikings . Amlaíb and Ímar . Viking activity in northern Britain appears to have reached a peak during Causantín ' s reign . Viking armies were led by a small group of men who may have been kinsmen . Among those noted by the Irish annals , the " Chronicle of the Kings of Alba " and the " Anglo - Saxon Chronicle " are Ívarr — Ímar in Irish sources — who was active from East Anglia to Ireland , Halfdán — Albdann in Irish , Healfdene in Old English — and Amlaíb or Óláfr . As well as these leaders , various others related to them appear in the surviving record . Viking activity in Britain increased in 865 when the Great Heathen Army , probably a part of the forces which had been active in Francia , landed in East Anglia . The following year , having obtained tribute from the East Anglian King Edmund , the Great Army moved north , seizing York , chief city of the Northumbrians . The Great Army defeated an attack on York by the two rivals for the Northumbrian throne , Osberht and Ælla , who had put aside their differences in the face of a common enemy . Both would - be kings were killed in the failed assault , probably on 21 March 867 . Following this , the leaders of the Great Army are said to have installed one Ecgberht as king of the Northumbrians . Their next target was Mercia where King Burgred , aided by his brother - in - law King Æthelred of Wessex , drove them off . While the kingdoms of East Anglia , Mercia and Northumbria were under attack , other Viking armies were active in the far north . Amlaíb and Auisle ( Ásl or Auðgísl ) , said to be his brother , brought an army to Fortriu and obtained tribute and hostages in 866 . Historians disagree as to whether the army returned to Ireland in 866 , 867 or even in 869 . Late sources of uncertain reliability state that Auisle was killed by Amlaíb in 867 in a dispute over Amlaíb ' s wife , the daughter of Cináed . It is unclear whether , if accurate , this woman should be identified as a daughter of Cináed mac Ailpín , and thus Causantín ' s sister , or as a daughter of Cináed mac Conaing , king of Brega . While Amlaíb and Auisle were in north Britain , the " Annals of Ulster " record that Áed Findliath , High King of Ireland , took advantage of their absence to destroy the longphort s along the northern coasts of Ireland . Áed Findliath was married to Causantín ' s sister Máel Muire . She later married Áed ' s successor Flann Sinna . Her death is recorded in 913 . In 870 , Amlaíb and Ívarr attacked Dumbarton Rock , where the River Leven meets the River Clyde , the chief place of the kingdom of Alt Clut , south - western neighbour of Pictland . The siege lasted four months before the fortress fell to the Vikings who returned to Ireland with many prisoners , " Angles , Britons and Picts " , in 871 . Archaeological evidence suggests that Dumbarton Rock was largely abandoned and that Govan replaced it as the chief place of the kingdom of Strathclyde , as Alt Clut was later known . King Artgal of Alt Clut did not long survive these events , being killed " at the instigation " of Causantín son of Cináed two years later . Artgal ' s son and successor Run was married to a sister of Causantín . Amlaíb disappears from Irish annals after his return to Ireland in 871 . According to the " Chronicle of the Kings of Alba " he was killed by Causantín either in 871 or 872 when he returned to Pictland to collect further tribute . His ally Ívarr died in 873 . Last days of the Pictish kingdom . In 875 , the " Chronicle " and the " Annals of Ulster " again report a Viking army in Pictland . A battle , fought near Dollar , was a heavy defeat for the Picts ; the " Annals of Ulster " say that " a great slaughter of the Picts resulted " . In 877 , shortly after building a new church for the Culdees at St Andrews , Causantín was captured and executed ( or perhaps killed in battle ) after defending against Viking raiders . Although there is agreement on the time and general manner of his death , it is not clear where this happened . Some believe he was beheaded on a Fife beach , following a battle at Fife Ness , near Crail . William Forbes Skene reads the " Chronicle " as placing Causantín ' s death at Inverdovat ( by Newport - on - Tay ) , which appears to match the Prophecy of Berchán . The account in the " Chronicle of Melrose " names the place as the " Black Cave , " and John of Fordun calls it the " Black Den " . Causantín was buried on Iona . Aftermath . Causantín ' s son Domnall and his descendants represented the main line of the kings of Alba and later Scotland .