My first conversation with director Neil Marshall was on set at Sheppeton Studios. We talked about Scottish folk music and instruments and I was immediately drawn to the idea of working with that musical heritage. I found a library of British folk music and started my research for Centurion looking at books of Gallic folk songs, learning the rhythms and melodic style and reading the poetry in the songs. Eventually I came across some old records to the furthest reaches of the British Isles. There they were able to capture the local people singing and telling tales of their ancient traditions and folklore; the recordings from Scotland were hugely inspiring and became the basis of many of the melodies in Centurion. The theme played on horns in the titles is a folk song about storms; it’s sung at various times in the film. This singing and whispering is the voice of the beautiful Pictish warrior Etain, who cannot speak. Her tongue was cut out by Roman soldiers and now she hunts them to their death. I needed a singer who was also an actor and could perform the role of Etain. Celia, with her distinct soprano voice alongside her stage experience and her Scottish background has a unique set of skills to bring this performance to life. Celia explored the Gaelic songs and dinging styles, and the studio sessions were full of inspiring ideas and unrepeatable performances ("Centurion" and "Funeral").

I also spent some time in the highlands, where I stayed at Inverlochy Castle. There I made a friend who was learning to play fiddle and she took me to a folk jam session in a pub. Over a few beers and several whiskies I was taught about folk music and told about ancient instruments. Somehow in the blur I scribbled down a few words to remember and in the morning the word carnyx stood out on the page. The carnyx had been talked about as a folkloric instrument, but after some searching back in London I found John Kenny, who plays the only reconstructed carnyx in the world. This instrument is the voice of battle in the film, not only was its sound utterly distinct with its high pitch wails or its huge scary low noises, but it was also entirely authentic to the period. The Picts would have played this instrument and the Romans would have heard it, and I imagine that the strange sound it makes must have been unnerving at best and terrifying at worst.

Often in the score, action music begins with percussion and carnyx solo ("Fort Attack" and "She Wolf"), the orchestra joining in later. The percussion was brought to life by Mike on the bodhran. This ancient Celtic instrument brought authenticity to the percussion and he also has a great solo in "Wolves." I approached the orchestral action music as though it was heavy metal. I wrote very fast tight strings with strict harmonic parallel movement, and the rhythm doubled precisely on drum, creating a rapid, accurate sound with a brutal attack. The precision of the performance in "Quintus Escapes" is remarkable. With this I wanted to reflect the method in which the Picts' attack the Romans, this use of the orchestra and drums with the carnyx and bodhran was the unsetting and violent musical atmosphere I imagined for the Pict warriors.

When we get to the sweeter moments in the film with Arianne ("Arianne" and "Quintus Returns") the music needed to give us a rest from the relentless action. I found another Gaelic folk song from the BBC archive. In the original recording it's sung by a woman, but with Etain already being a female voice I needed to find a different instrument. The delicate tone of the Celtic harp was perfect for the very pretty and graceful Arianne. The harpist Gill, with whom I have worked many times, brought the sensitivity and charm that the scenes need.

One of the major challenges was the adagio that Neil wanted over the slaughter of the Ninth Legion. The drama of the scene needed to rise grow but at the same time it is an emotional descent; a monumental loss of human life. This moment is central to the entire story which is imagined around the infamous disappearance of the Ninth Legion. That this story echoes from Roman times to present day is testament to how extraordinary an event it was. I conceived the adagio ("The General Falls" and "The Fate Of The Ninth") around the idea of ascending and descending scales, allowing notes collide, like the people fighting on the screen, and in turn this created suspensions and resolutions as the notes pass through each other. This idea of things pulling in different directions, opposing forces, like magnets, is an important theme of the film. The Pict warriors are actually farmers, the Ninth Legion were meant to going home, the Roman survivors must venture deeper into the highlands before they can get back to safety and both Arianne and our hero Quintus, despite being virtuous are rejected by their people. The adagio is the emotional core of the film, whilst the Gallic themes and traditional instrumentation bring authenticity to the style of the score.

Film music is always collaborative and working with the film makers, my extraordinary team and the London Metropolitan Orchestra made this music possible. I hope you enjoy listening to it as much as we enjoyed creating it.