AN ACCIDENTAL discovery has shed new light on the workmen who helped build an ancient Scottish cathedral.
The 12th-century St Magnus Cathedral in Kirkwall is the most northerly in Britain.
Hundreds of distinctive symbols, including marks left by the building's original stonemasons, are scattered throughout the interior of the Viking cathedral, situated in the heart of the Orkney capital.
In near constant use as a place of worship, a tourist site and a venue for concerts and other events, the building has been extensively studied and documented over the years.
But an upgrade to the cathedral's lighting system has revealed previously unnoticed marks on archways, believed to have been left by stonemasons more than 600 years ago when the entrance was extended.
According to cathedral custodian Julie Marwick, the newly discovered marks are thought to date from the late 14th or early 15th century.
"It was really quite exciting," she said. "Although there are over 100 different marks that have been found throughout the cathedral, we've never found so many on one arch.
"They only became visible once the new lighting was installed because we've now got uplighters. It was like 'Wow, where did they come from?'"
For the current cathedral stonemason Colin Watson, the marks are a tangible link to his ancient counterparts.
"The feeling is you're connecting with the guys who made the stone that's there," said Mr Watson, who has worked on the cathedral for the past 25 years and has his own mason's mark. "You wonder what was in their head when they set out to make the stone.
"Before the days of contracts, masons were paid for the work they did, so when they made a stone, they marked it and that meant they got paid for it.
"If it didn't fit, or if it was wrong in any way, they knew the mason through his mark and knew who to shout at. Basically, it was a form of identification for payment."
Work on the cathedral started in 1137, founded by the Viking earl Rognvald in honour of his martyred uncle, St Magnus. The remains of both are set within the building's pillars.
Between 1154 and 1472, Orkney was ecclesiastically under the Norwegian archbishop of Nidaros (Trondheim) and later became part of the Scottish province of St Andrews. The cathedral was assigned to the inhabitants of Kirkwall by King James III of Scotland in a charter dated 1486.
Today the distinctive sandstone landmark, known as the Light in the North, receives more than 70,000 visitors a year.
Although used mainly by the Church of Scotland for services, the cathedral belongs to the local community rather than the church.