The earliest written reference linking such creatures to Loch Ness is in the biography of Saint Columba, the man credited with introducing Christianity to Scotland. In A.D. 565, according to this account, Columba was on his way to visit a Pictish king when he stopped along the shore of Loch Ness. Seeing a large beast about to attack a man who was swimming in the lake, Columba raised his hand, invoking the name of God and commanding the monster to "go back with all speed." The beast complied, and the swimmer was saved.
When Nicholas Witchell, a future BBC correspondent, researched the history of the legend for his 1974 book The Loch Ness Story, he found about a dozen pre-20th-century references to large animals in Loch Ness, gradually shifting in character from these clearly mythical accounts to something more like eyewitness descriptions.