History of Scotland: Development of Christianity
Saint Ninian and Saint Kentigern were among the earliest Christian missionaries known to have worked in Scotland, but the Irish Scot, Saint Columba, probably did most to Christianize the Highlands from his base on Iona during the second half of the 6th century.
The Celtic Church was a powerful missionary body, but it lacked the close-knit Roman organization. Defeated at the Synod of Whitby (664), the Celtic clergy retired to Scotland and within half a century both Picts and Scots had accepted the Roman supremacy. and customs. Dunkeld, the ecclesiastica capita, was soon superseded by St. Andrews. Saint Margaret, an English princess who married Malcolm III, did much in the late 11th century to bring the Scottish Church into closer touch with the reforms effected in the Roman Catholic Church.
Under her sons, who reigned in the first half of the 12th century, regular dioceses were developed, Continental orders of monks were introduced, and a parochial system started. The payment of tithes for the support of parish church was made compulsory.
The youngest of Queen Margaret's sons, Dav I (reigned 1124-1153), had spent much time the English court and had married an English heiress. He reorganized the whole fabric of the Scottish Church and state on Anglo-Norman lines. The old Celtic use of collateral succession to the crown was replaced by primogeniture.
Land was granted to Anglo-Norman nobles, who held it from David I and acted as his lieutenants in the maintenance of law and order. Sheriffs were established in the royal castles to do justice, collect taxes and rents, and generally carry out the king's orders, while many burghs were created to serve as military strongholds and trading posts. Particularly in the north, the new system supplemented rather than replaced the old Celtic practices, but even there it proved a unifying factor.