So, let's start at the origin, where it came from. The Loch Ness monster, or Nessie, was first mentioned in 565 AD in the "Life of St. Columbia". This is a book, written by Adomnán. In the book, a man ends up going into the water after seeing another man die to the beast. When the man goes into the water the beast approaches him he makes a cross with his arms and the beast leaves.