A HISTORIAN has unveiled another mystery in the depths of Rosslyn Chapel - an ancient navigational sign.

Ashley Cowie stumbled across the symbol, in the chapel's crypt, while researching a book. The icon illustrates a long-forgotten method for measuring time and distance used by ancient Norse people.

The chapel, which features in Dan Brown's bestselling book The Da Vinci Code, has experienced a tourist boom in recent years.

The novel follows a trail to unearth Christ's bloodline, which eventually leads to Rosslyn Chapel, near Edinburgh.

Mr Cowie, from Caithness, has spent the past decade deciphering the carvings in the landmark for his book, The Rossyln Matrix. Now, in the underground crypt featured in the Da Vinci Code film, he has unearthed a symbol illustrating the long-forgotten measuring system.

The sign is a navigational aid, likely to have been passed by ancestors to the Earl of Rosslyn, William St Clair, who built the chapel in the 15th century.

To the layman, the etching looks like a miniature electricity pylon, but it has global significance for the history of navigation. The long-forgotten method of measuring time and distance is represented on the wall of the crypt.

At the top is the outline of a misshapen cup which has a five-pointed star on one sides. Inside the cup are four diamond-shaped lozenges of different lengths and widths stacked on top of each other.

Mr Cowie believes the lozenges, which are based on shadows of the sun, are different shapes to represent different lines of latitude. The pylon shape is a line of longitude, and the cup symbolises the orbit of the planet Venus.

He said: "What is down there is an example of a lost system for measuring time and distance involving both latitude and longitude. It's a priceless mapping treasure. All this was important to ancient navigators for synchronising dates, times and locations."

However, Stuart Beattie, from the Rosslyn Chapel Trust, said: "The trust does not align itself with any theories surrounding the chapel. They are interesting theories but they have yet to be proven."