As noted before, the expansion of Dalriada was accomplished not so much by invasion, as by the joining together in marriage of the Dalriadans and the Picts. The two kingdoms of Picts and Dalriada/Scotti would practically fall into place by the year 844 AD. In that year Cinaeth, or Kenneth, MacAlpin unified the two into the single Kingdom of the Scots.
According to Norman Davies in his book, The Isles ~ A History: “By the early ninth century, the relationship of Dalriada to Pictland was characterized by an odd combination of political subservience and culteral ascendancy.” (2.62) In regard to the first part of Davies’ so-called ‘odd combination,’ three Dalriadan kings married Pictish princesses (it was a Pict custom for kings to have their daughters married to important foreigners) and so made their way into the Pictish ruling lines. It was the third one, Cinaeth, son of Alpin, who seized the opportunity and wrested control of the Picts from his father-in-law, and became king of both Pictland and the Scots. The second part was the result of the spreading of Christianity by Gaelic speaking Irish monks. It served to consolidate the Gaelic language as the means of communication between the Scots and the Picts. Along with the Gaelic language came ‘Gaelic’ customs and laws, and via the bards and storytellers came ‘Gaelic’ history, mythology and legends.
Kenneth MacAlpin brought the Stone of Destiny from Eire and had it installed in the church at Scone (hence its one alternate name) for his own inauguration. The act was perhaps somewhat of a conciliatory gesture on the part of Kenneth toward his own mother’s Pict ancestors; Scone was the seat of the Pictish kings. From that point to the present time, the kingdom forged by Kenneth would be known neither by the name of Pict nor Dalriada, but rather as Scotia, or Scotland. Upon the Stone of Destiny the High Kings of Eire had been, and later, Scotland would be crowned.
2.62 The Isles – A History, by Norman Davies 1999, p 191.