IT was the ancient symbol of Edinburgh, and was raised whenever the city’s tradesmen were called upon to defend the king.
According to legend, the Blue Blanket banner was first flown from the walls of Jerusalem by Edinburgh crusaders in the 12th century.
But during the last 100 years the banner has been seen by only a handful of people and, despite its historic significance, it has never gone on display in the city’s major museums.
Now talks are under way between museum chiefs and an obscure and ancient Edinburgh society to display the priceless relic in the National Museum of Scotland in Chambers Street.
The banner is owned by the Incorporated Trades of Edinburgh, which represents the 14 ancient "guilds" of the city.
The guilds, representing ancient crafts such as fleshers, hammermen and skinners, were a powerful force in the city during medieval times.
The guilds still meet regularly at their New Town headquarters, the Trade Maidens Hospital, with the Blue Blanket hanging in the corridors of the three-storey house.
Now the guilds are considering loaning their most prized possession to the National Museum, which wants to display it alongside its own version of the Blue Blanket - which experts believe is a copy of the original.
The National Museums of Scotland today confirmed that talks were under way to secure a loan of the blanket.
A spokesman for the guilds said: "The Blue Blanket is really a priceless artefact. It is an important symbol of Edinburgh’s history and we believe it is something that the people of Edinburgh should take an interest in. We have had people from the National Museum over to see it and they seem quite keen on displaying it.
"We would have to make sure that it was transported and stored safely as it is not something we could ever replace."
Historians Ian Robertson and Professor Karen Ralls-MacLeod wrote about the blanket in their book, Quest for the Celtic Key.
Mr Robertson said today that there were various copies of the Blue Blanket around the world, but that the guilds have the "real McCoy".
He said: "Whether or not it goes back to the Crusades we cannot say, but it is said to date back at least to 1482, when King James III was rescued from Edinburgh Castle by the city’s tradesmen after being imprisoned by nobles.
"This is a tremendously important part of the city’s past and it would be great to see it displayed in the National Museum." The history of the blanket was written down for the first time in 1722 by historian Andrew Pennecuik.
He claimed that tradesmen from the city joined the Crusades in the 12th century, and took the Blue Blanket with them. It contained words from the 51st psalm: "I thy good pleasure build the walls of Jerusalem."
On returning to the city the tradesmen adopted the banner and formed the Order of the Blue Blanket, said to be the oldest order of chivalry in Europe, with an altar at St Giles’ Cathedral.
In the 1890s it was publicly displayed for the last time when the Town Guilds welcomed Queen Victoria to the city.
Since then it has been stored in the Trade Maidens Hospital, which was set up to help city girls who fell on hard times but now acts as the home of the guilds.