His reign, like those of his predecessors, was dominated by the actions of Viking rulers in the British Isles, particularly the Uí Ímair ('Grandsons/Descenants of Ímar', or Ivar the Boneless).

At first, the southern rulers allied with him against the Vikings, but in 934, Æthelstan, unprovoked, invaded Scotland both by sea and land with a huge retinue that included four Welsh kings.

Constantine's reign of 43 years, exceeded in Scotland only by that of King William the Lion before the Union of the Crowns in 1603, is believed to have played a defining part in the Gaelicisation of Pictland, in which his patronage of the Irish Céli Dé monastic reformers was a significant factor.

Originally simply a list of kings with reign lengths, the other details contained in the Poppleton manuscript version were added in the 10th and 12th centuries.

[2] The earliest genealogical records of the descendants of Kenneth MacAlpin may date from the end of the 10th 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.

[4] While Scandinavian sagas describe events in 10th century Britain, their value as sources of historical narrative, rather than documents of social history, is disputed.

[6] While 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.

By the 9th century, the Gaels of Dál Riata (Dalriada) were subject to the kings of Fortriu of the family of Causantín mac Fergusa (Constantine son of Fergus).

[9] Later national myth made Kenneth MacAlpin the creator of the Kingdom of Scotland, the founding of which was dated from 843, the year in which he was said to have destroyed the Picts and inaugurated a new era.

Among the chief ecclesiastical centres named in the records are Dunkeld, probably the seat of the bishop of the kingdom, and Cell Rígmonaid (modern St Andrews).

[13] In 899 Alfred the Great, king of Wessex, died leaving his son Edward the Elder as ruler of England south of the River Thames and his daughter Æthelflæd and son-in-law Æthelred ruling the western, English part of Mercia.

Donald's reputation is suggested by the epithet dasachtach, a word used of violent madmen and mad bulls, attached to him in the 11th-century writings of Flann Mainistrech, echoed by his description in The Prophecy of Berchán as "the rough one who will think relics and psalms of little worth".

[26] The earliest event recorded in the Chronicle of the Kings of Alba in Constantine's reign is an attack by Vikings and the plundering of Dunkeld "and all Albania" in his third year.

This is the first use of the word Albania, the Latin form of the Old Irish Alba, in the Chronicle which until then describes the lands ruled by the descendants of Cináed as Pictavia.

The Fragmentary Annals of Ireland contain an account of the battle, and this attributes the defeat of the Norsemen to the intercession of Saint Columba following fasting and prayer.

[34] The idea that this gathering agreed to uphold Irish laws governing the church has suggested that it was an important step in the gaelicisation of the lands east of Druim Alban.

Æthelflæd had been negotiating with the Northumbrians to obtain their submission, but her death put an end to this and her successor, her brother Edward the Elder, was occupied with securing control of Mercia.

In the south, Alfred's son Edward had rapidly secured control of Mercia and had a burh constructed at Bakewell in the Peak District from which his armies could easily strike north.

Here, again, a new term appears in the record, the Anglo-Saxon Chronicle for the first time using the word scottas, from which Scots derives, to describe the inhabitants of Constantine's kingdom in its report of these events.

William of Malmesbury writes that Gofraid, together with Sihtric's young son Olaf Cuaran fled north and received refuge from Constantine, which led to war with Æthelstan.

A meeting at Eamont Bridge on 12 July 927 was sealed by an agreement that Constantine, Owain, Hywel Dda, and Ealdred would "renounce all idolatry": that is, they would not ally with the Viking kings.

Owain was defeated and Symeon states that the army went as far north as Dunnottar and Fortriu, while the fleet is said to have raided Caithness, by which a much larger area, including Sutherland, is probably intended.

It is unlikely that Constantine's personal authority extended so far north, so the attacks were probably directed at his allies, comprising simple looting expeditions.

[54] The Annals of Clonmacnoise state that "the Scottish men compelled [Æthelstan] to return without any great victory", while Henry of Huntingdon claims that the English faced no opposition.

The following year, Constantine was again in England at Æthelstan's court, this time at Cirencester where he appears as a witness, as the first of several kings, followed by Owain and Hywel Dda, who subscribed to the diploma.

When reporting the battle, the Anglo-Saxon Chronicle abandons its usual terse style in favour of a heroic poem vaunting the great victory.

Æthelstan's realm, seemingly made safe by the victory of Brunanburh, collapsed in little more than a year from his death when Amlaíb returned from Ireland and seized Northumbria and the Mercian Danelaw.

Unlike the report of 918, on this occasion, the title mormaer is attached to a geographical area, but it is unknown whether the Angus of 938 was in any way similar to the later mormaerdom or earldom.

The kingdom of Alba was too new to be said to have a customary rule of succession, but Pictish and Irish precedents favoured an adult successor descended from Kenneth MacAlpin.

[64] Seven years later the Chronicle of the Kings of Alba says: [Malcolm I] plundered the English as far as the river Tees, and he seized a multitude of people and many herds of cattle: and the Scots called this the raid of Albidosorum, that is, Nainndisi.