"Do not talk to the bus driver while he's driving," it says in German above the windshield, although the bus is driving through Albania. Forty years before, it was brand new and rolling along German roads. Now it's transporting a choir and an orchestra from Tirana to Shkodër. Huge decaying factories surface from the winter fog in beautiful valleys, shattered greenhouses and one little round bunker after the next, cover the countryside like a rash. Blood on the side of the road. A cow twitches in the grass. It was slaughtered in the open for New Year's Eve. We saw no end of animal parts dangling from telephone poles. And in my head like a soundtrack to the film, I could hear music we were touring with: the Credo of Bach's Mass in B Minor.

This fugue is particularly likely to stick in a violia player's mind. This is not a viola player joke: it's just that one of the most beautiful pieces that Bach wrote for viola player allows them to just sit back and listen. The Credo comes in the middle of the mass. If you had been suffering from toothache before the performance, your pain will be numbed; if you feared death, you will fear it no longer, if you had no religion, you will no longer need one. The horizontal of time, the ephemera, becomes a vertical, a frozen moment in whose expanses an inexplicable feeling of comfort arises. And then comes the Credo. The tenor sings first and then the cembalo and the basses begin to feel their way along under the long notes.

Eight quarter notes per bar, up and down in a myriad little steps, an unflagging little hill-walker, and on the other side, the five-toned glory. It's earthy and emotional, this doggedly human effort of the basses against the weightless vocal horizon. This unfurls smoothly, the way a fixed horizon gradually transforms when seen from a moving bus. It's panoramic music which offers endless space for new views of the world. And while the violins trace golden contour lines, the violas listen for 45 bars, silent witnesses of this balancing of worlds. The centre is reached, the instrument in the middle has nothing more to do. Now the strings join in, inaudibly. Bach understood that. His son Carl Philipp Emanuel wrote: "As the best expert and judge of harmony, his instrument of choice was the viola..."

Maybe he saw the wide world before him as he travelled the brief stretch between Eisenach and Leipzig, and rarely beyond. The world in which his notes would travel. There is no music that has travelled as far and as well as his; it was already suited for the tropics by the time Albert Schweitzer set up his special moisture-resistant piano in the jungle. Bach is suited to all climatic zones, as long as the players don't pass out. When you've been travelling with his music for a while, in the southern hemisphere or through the churches of Thuringia, you feel as though he's sitting in the bus beside you, a quiet travelling companion, friendly, not the tour leader type, not the diva who's always gets sick first, but someone who, to everyone's surprise, has a can of beer in his bag that he's willing to share.

In Mexico, he saved us. We sat in the theatre in Guadalajara, a city of three million, in front of an old stage backdrop, an enormous, ragged screen. A bucolic scene was painted on it and it was breathing. Between the cooling air from the street and the warm moist breath of the huge, silent audience, the entire painted landscape heaved slowly back and forth. At some point it seemed to me as if the audience too was oscillating in the half-darkness, except for four half-naked Mexican beauty queens, adorned with sashes, frozen with pride, sitting in the front row. A sight like that can make you dizzy.

We started by playing cantatas by Bach's predecessors: "Caminos que conducen a Bach". The reaction hardly suggested that the people of Guadalajara had been waiting all their lives to hear protestant Baroque. They're so Catholic that there was even a picture of the Madonna at the back of the side stage, adorned with fresh flowers. But when Bach himself arrived, the connection was there. "Christ lag in Todesbanden" is a furious fight against death. Bach was 23 years old when he wrote it. Three of his siblings, both his parents, and most recently his ingenious uncle Johann Christoph had all died. The latter seems to be there with him still, helping compose the prelude full of painful chromatics. Then the young composer sets out to fight the one "den niemand zwingen kunnt", which nobody can coerce. His choral variations encircle death in siege, bright with confidence and blossoming fantasy. Bach has not yet disappeared in his music here, he encounters death himself, on this side, like the Mexicans who sell skeleton marionettes in the market and skulls of sugar: "Ein Spott aus dem Tod ist worden", death has become a mockery.

The whole piece swings. It is full of joy. When we finish the seventh and last verse, the people spring up in the semi-darkness, ecstatic, as though we had just played some Mexican hit and not a three hundred year old cantata. The four beauty queens want autographs. Even from us viola players.

No one make us mid-toners feel so needed as Bach. Many consider viola players the wall flowers between the violins and the cellos, the stop-gaps who get to play the odd filler notes or double the bass and can't do much more anyway. That's because a few decades ago, we really were a little under-employed, when polyphony went out of fashion, a process that had already begun in Bach's lifetime and then continued through the Viennese classical era – although Mozart gave the viola a few wonderful passages. But actually the 18th century after Bach was not especially keen on the middle voices and their diplomatic skills, the tones that mediate between extremes, the heights and the depths, the far and the near.

In the ruptured 17th century that spawned Bach, the viola player was much loved. Claudio Monteverdi took up the viola himself. It was not uncommon for there to be three viola players for every violinist. Luxurious, dense, warming multi-vocality, comforting in an era of wars and plagues and the new realisation that the earth has no fixed position but in fact rotates around the sun. Maybe the middle tones helped compensate for the loss of the middle. Towards the end of the century, the instrumentation for the cantatas was two violins and two violas (or viola da gamba) over the bass standard, and Bach's "Christ lag in Todesbanden" was also performed in this way.

Bach soon departed from the dual-viola instrumentation but the one he held on to, under the violins, seemed to gain in beauty. It had all the lovely features that Bach's lines always have; even when you play it alone, you can hear the rest of the work, assuming you know it. With the works of other composers, Purcell being a possible exception, it's rare for one part to evoke the entire context in which it is heard. So it's pure pleasure to practice Bach. And when you rehearse together, there's no reason to envy the others because they have something better. To the contrary: even the violinists admit that the viola often has the most interesting role. Bach played it himself, in the words of his son, "with the appropriate strength and weakness," always working out the course of the harmonies.

And he often sets the key stone, the moment that all the tension is leading up to and which makes the piece waterproof in the end, by taking the viola from minor into major or brushing a little third from a major chord. It also has its own personality in the B minor mass. After the great invocation "Kyrie eleison," the orchestra plays for 25 bars alone. The viola continually provides the basic rhythm with a little anacrusis that spans the tightest intervals up to the tritone. This will largely escape the attention of the listener, at best he might notice that the viola players look a little more motivated that they do, ehem, at the beginning of Handel's "Messiah". What he will hear, though, is the luxury that Bach bestows on us in "Et in terra pax". Seven bars before the end, the viola starts up a series of sixteenths, and the only thing this has in common with anything that came before is the scale traversing. A Byzantine, sumptuous shimmering ribbon effuses from the viola, an almost exoticly bright inlay, before the familiar motive returns to end the piece.

When viola players play that the way they'd like to, they can be sure that the conductor will soon quieten them down. But there's another passage in this mass, where they truly play the central role. In it, the viola carries the sins of the world for fifty bars, reminiscent of an ancient, sorely afflicted, timeless and gentle lamb. Bach leads us in inescapably, because the "Qui tollis peccata mundi" begins before it begins: the last notes of the piece become the prelude, it becomes a syncope and then our heavy procession begins. The choir sings softly of the sins of the world and begs for mercy, the flutes wallow in redemption, but the viola has to do the work, bearing the yoke of unremitting pairs of eighths.

These lead into the most dangerous of harmonies, and if you can't play them sprucely you might as well pack your bags – you hear every note. And as you play you sense how Bach worked to boost his and our confidence alike. You must travel a path with the "Agnus Dei," the lamb of God. You doesn't necessarily have to think of Jesus, this is about all the weight and pain of the world and how we bear it. In the spoiled cities of Europe where the mass is part of the repertoire, the existentialism in these few bars of suffering is barely heard. But when we play this in Albania, it is needed. Everything that somehow offers comfort is welcome and Bach's great mass has never been played here before.

"Are you really playing the B minor mass?" asked a composer in Shkodër, a little city in the north. "With everything? With Credo and Osanna and Sanctus?" He knew the work only from the sheet music and the radio. And we played it in a theatre which, in Germany, would have been closed by health and safety long ago. From below the stage, a light glimmered through the planks of an ancient revolving stage, on which were glued the remnants of props from a variety show. The light flickered, but it didn't go out. Behind the theatre was a hut with a diesel generator which produced very noisy electricity. The strings were moist from the rainy weather and out of tune, but it was alright. It's always alright when the audience is so excited.

It's not just the audience which profits when Bach tours these musically under-nourished communities. The musicians themselves discover him anew, experience him free of the freight of bourgeois ritual. Nothing against the countless masses, oratorios, cantatas, Brandenburg concertos in well-heated churches and halls, in richly illuminated shopping zones, nothing against the musical hearth god of academic families from Paris to Tokyo, but at some point, you want to to hear these compositions in the open as it were, not embedded but exposed. When it does come to this, Bach is well ahead of us. The calm fellow traveller was a linguistic genius, he had made contacts at every level before we even learned to say "please" in the local language.

But around the corner in his homeland, he's not so popular. Presumably the Thuringians are proud of Bach but maybe they're wary of the shadow he casts. On the edge of the Thuringian Forest there's a town called Themar with just over 3,000 inhabitants and a beautiful late Gothic church. When we'd changed and were standing around in front of the church, a couple of kids cycled past and, seeing our black suits, one called to the other: "Another one dead in this shitty town". Bach didn't die that evening, although his work was only heard by seven elderly women. This just makes you play fervently for all eternity, comforting yourself with the thought that even in the poorest, most forgotten gold rush towns in southern Australia, the hall fills when Bach rolls in.

Or in the mining town of Forbach in Lothringen, another place that has not exactly been spoiled by the times but which – nomen est omen - harbours an enthusiastic passion for Bach. There, my viola fell in love with his motets that barely need it at all. They were written for highly versatile singers whose voices in, at least one documented case, Bach accompanied with instruments – the orthodox performance ideal of one true version is after all, a fiction of the art cult of the 19th century. As an instrumentalist, one is intimately close to the singers here. The filigree phrases, which bend to follow the words, force the bow to speak more sensitively the syllables, words, phrases, than one normally does with Bach. The motets fail if they sound muddy and oratorical, but they pierce your heart if they're focussed and lean.

The singers and their stringed accompaniment were stacked up on a steep landing in the packed church in Forbach. Behind me was a gaping hole with a stone column for support. Yet another reason to play forward, into the heated appetite of the audience. Because Bach's music always connects with its environment and absorbs all impressions, I can still savour in the motets the aromas of what the Forbachers served afterwards: steak and red wine.

And the "Agnus Dei" carries on its back the memory of that day when it could go no further in Albania. We were rehearsing the B minor mass in the capital, Tirana, in a pyramid. This had been built as a memorial by the communist dictator Enver Hoxha, and has now become a cultural centre with candelabra and mirrors. But when the lamb started out on his arduous journey with the eighths from the viola, the lights went out. We fared a little further playing from memory, but then the lamb dissovled into scrawny tones and disappeared into the darkness. If this was supposed to be the revenge of the atheist Hoxha, then he must have reconsidered by the time of the concert. The mass took place illuminated. Including the most lovely pause ever created for the viola player...

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Volker Hagedorn recommends the follwing CD: Magnificat in E flat major BWV 243a. Rheinische Kantorei/Das Kleine Konzert, under Hermann Max (emi). Works better than a double espresso, apparently.

This text originally appeared in the March 2006 issue of DU magazine.

Translation: nb.