MAGNUS Erlendsson was a gentle soul, or at least he was according to the legends. His life is told in the epic Orkneyinga Saga: how he ruled as a compassionate Earl of Orkney for just over a decade at the start of the 12th century, how he had a reputation for piety which the Norwegians laughed off as cowardice, how he was murdered on Egilsay by his cousin Haakon Paulsson then martyred by his nephew Rognvald Kali Kolsson and his relics laid as the foundations of St Magnus Cathedral in Kirkwall. His death was in 1117. Eight and a half centuries later, the Stromness writer George Mackay Brown wrote a richly poetic novel called Magnus in which he drew parallels between the Orkney saint and the philosopher Dietrich Bonhoeffer, who was murdered by the Nazis during the Second World War.

There’s a lovely hymn dedicated to St Magnus, too, which is probably the oldest surviving evidence of harmony we have in Scotland. It’s a 12th century plainchant called Nobilis Humilis whose Latin manuscript was penned (or quilled, strictly speaking) in St Magnus Cathedral and is now kept in Uppsala University in Sweden. The voices rise and fall in tranquil parallel thirds: “Noble one, humble one, you the martyr’s course have run/ Gentle one, helpful one, your merit we revere.”

This simple tune has been noticed before. When he first moved to Orkney in the early 1970s, the composer Peter Maxwell Davies integrated Nobilis Humilis into his own Hymn to Saint Magnus, which was the first major piece he wrote from his storm-battered little home on Hoy. The music is full of the brutality of martyrdom and the rugged violence of the sea, but also with serene handbells and soft sounds. I love the anomalous image it creates: Magnus, that gentle Viking, that pacifist warrior.

And now Nobilis Humilis has become the starting point of a whole programme of new choral pieces called Echoes and Traces. Eight Scottish composers have been sent the hymn and asked to respond with a work for 12 voices lasting around eight minutes. The brief, as far as I can glean, was no more specific than that, so the results should hopefully be nicely multifarious. The programme will be premiered by Cappella Nova in Dunfermline Abbey then toured around historic venues including St Magnus Cathedral.

Instigator of the project is the harpist and composer Ailie Robertson, an Edinburgh-based musician who spans traditional and contemporary classical idioms and who set up a contemporary music company called Larimer Productions precisely to make programmes like Echoes and Traces come to fruition. She tells me that she chose the seven other composers (she has written one of the new works herself) with the aim of representing a range of stylistic backgrounds and an equal gender balance. “And let’s be honest,” she grins, “to get my own name in the same programme as some of my favourite musicians.”

So how have the eight composers responded? Hanna Tuulikki – herself a vocalist as well as a composer and visual artist – focuses on themes of pacifism, and a passage in the Orkneyinga Saga that describes the young Magnus refusing to take up arms during the Battle of Anglesey and instead remaining on board his ship singing psalms. (George Mackay Brown’s novel describes the scene vividly, and how Magnus’s fellow fighters are none too thrilled with his singing). Tuulikki uses approximations of the extinct Norn language that would have been spoken in 12th century Orkney: sju for sea, swaal for sea swell, laar for a light breeze.

Fiddler/composer Aidan O’Rourke also turns to Norn in his piece, or rather to its closest living equivalent: Av sonnum hevur hann hogt erpnu halsar teirra heidnu – that’s the first line of the hymn, for anyone not quite fluent in Faroese. Turns out that the guttural, consonant-rich language of the Faroe Islands does similar things to Gaelic when set for voices. Stuart Macrae goes for a blend of Latin and English in order, he says, to shift our attention to different expressive moments in the text. He points out that this is a hymn and a history that sit on the brink: Vikings and Catholics, the end of Magnus’s life and the beginning of his legacy through the new Cathedral.

Rory Boyle takes the music rather than text of the hymn as his starting point and makes a feature of those beautiful lilting thirds, uses them to create what he describes as “thicker blurring textures”. For Ailie Robertson’s own contribution, she felt it important to reference Magnus’s Viking-ness so she weaved in a Swedish traditional song called Ho Sitt a Gillan as well as Celtic drones and ornamentation.

Savourna Stevenson retained the melody of the hymn and asked the writer Les Barker to provide a narrative. “Magnus’s epic and involuntary journey from Orkney down through the Hebrides, Northern Ireland and the Isle of Mann; warfare and pillage all the way to their accidental encounter with a Norman army on Ynys Seiriol.” That’s the battle where Magnus stayed on the boat and sang. Barker homed in on a line in Psalm 88 (“shall the dead arise and praise thee”) which, says Stevenson, “led us through centuries of warfare and intolerance, down to today and to the hope that one day we’ll realise we’re all one people.”

When Robertson first started planning Echoes and Traces, she had hoped the programme might include a new piece by Maxwell Davies, a chance for him to revisit the old hymn he set four decades ago. In the end he didn’t live to write the commission but he is present in Sally Beamish’s piece Saint’s Day, which she dedicates to her “friend and mentor”. Beamish doesn’t use the text of the hymn; instead she chooses words by George Mackay Brown, who once wrote that “the essence of Orkney’s magic is silence, loneliness and the deep marvellous rhythms of the sea and land, darkness and light.”

The poem that Beamish sets is called April the Sixteenth – Magnus’s saint’s day – which she felt embodies those deep marvellous rhythms of the sea and land. Here, then, is a taste: “What have they brought to the saint?/ The shepherds a fleece./ That winter many lambs were born in the snow./ […] And the poor of the island/ Came with their hungers/ Then went hovelwards with crossed hands over the hill.”

Echoes and Traces is at Dunfermline Abbey tonight, Stirling Castle tomorrow, then Glasgow Cathedral (September 2), Duff House, Banff (September 4), St Magnus Cathedral, Kirkwall (September 5), Iona Abbey (September 7) and Greyfriars Kirk, Edinburgh (September 8)