Constantine II of Scotland was an early King of Scotland, known then by the Gaelic name Alba. His reign, like those of his predecessors, was dominated by the actions of Viking rulers in Britain and Ireland, particularly the Uí Ímair. During Constantine's reign, the rulers of the southern kingdoms of Wessex and Mercia, later the kingdom of England, extended their authority northwards into the disputed kingdoms of Northumbria. At first allied with the southern rulers against the Vikings, Constantine in time came into conflict with them. King Æthelstan secured Constantine's submission in 927 and 934, but the two again fought when Constantine, allied with the Strathclyde Britons and the Viking king of Dublin, invaded Æthelstan's kingdom in 937, only to be defeated at the great battle of Brunanburh. In 943 Constantine abdicated the throne and retired to the Céli Dé monastery of St Andrews where he died in 952. His 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. During his reign the words "Scots" and "Scotland" (Old English: Scottas, Scotland) were first used to mean part of what is now Scotland.