(CNN) — "Silent Night" might be one of the sweetest Christmas carols there is, but following the trail of the man who wrote it exactly 200 years ago involves an unexpectedly macabre twist.

"The skull is embedded behind there," says guide Sepp Greimel, pointing at a nativity scene over the altar of the chapel we're stood in.

The skull, mercifully not visible, belongs to Josef Mohr, Catholic priest and joint composer of the Christmas carol that has been translated from its original "Stille Nacht" into more languages than there are countries in the United Nations.

Its final resting place, the small Austrian town of Oberndorf bei Salzburg, is aptly named for his most famous verse: the Silent Night chapel.

In midwinter, a visit here is a truly festive experience.

Despite its rural Austrian chocolate-box style exterior, the church's interior is rather bare: a larch ceiling, fir pews to sit 22 and a pink-red marble floor hewn from a nearby quarry.

The only decorations are the two small stained glass windows with images of Mohr, who wrote the lyrics, and Franz Xaver Gruber who composed the music to "Silent Night." Two plain portraits of the men adorn the wall.

There's also a framed copy of their famous song -- just six stanzas, but apparently three too many when sung in its original language.

"We only sing stanzas one, two and six," Greimel says. "Stanzas three, four and five are difficult to sing in German."

The chapel -- simple, like the song -- was built to replace the parish church of St Nicholas where Mohr served as a curate and where the song was first performed 200 years ago, on Christmas Eve, 1818.

To explain why the original church was demolished, Greimel leads the way outside.

Divided by war and water

The German town of Laufen stands across a U-bend in the Salzach river. John Malathronas

Snowflakes are falling mutely on the old center of Oberndorf, which is already covered in a dusting of snow. The scene is so Christmassy it wouldn't be a surprise to see Santa Claus descending from the heavens in a sleigh.

From the top of a nearby levee, the river Salzach can be seen making a large U-bend only a few hundred yards from the chapel. Beyond it, the picturesque town of Laufen lies over the border in Germany.

It wasn't always so.

Oberndorf, along with Laufen, once belonged to the Bishop of Salzburg for centuries until the Napoleonic wars of the early 19th century. Subsequent frontier changes divided them between Austria and Germany.

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They had both prospered from the river trade in salt, especially since a large boulder in the bend, known as Nocken, forced barges to stop here, unload and reload.

The Salzach was the blessing of the two towns, but also, thanks to frequent floods, their curse -- hence the levee.

"There was a terrible flood here in 1899," Greimel says, his voice trembling as if he'd experienced it himself. "It destroyed the old Oberndorf center.

"The villagers then decided to build a new church 600 yards to the south, on higher ground."

It was an earlier flood that was responsible for "Silent Night." For the full story, it's time to go back to the beginning.

Executioner's exit

A model of Franz Xaver Gruber and a portrait of John Mohr, the composer and the lyricist behind "Silent Night." John Malathronas

Mohr was born out of wedlock in 1792 in the nearby city of Salzburg, the son of a seamstress and an army musketeer, according to local history expert Michaela Muhr.

One of his first homes still stands at number 31 Steingasse, a plain terraced house on two floors in the poorest part of town.

Steingasse is a cobblestoned street, one carriage's width, with buildings rising high either side, permanently in shade, except when the sun stands directly above at noon.

"Because he was illegitimate, it was difficult to find godparents to baptize him," says Muhr. "Only the town hangman agreed. He was keen to make up for his executions, but even he sent his housekeeper instead."

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Baptized in the same font as Mozart, Mohr later began to grow into a child of sufficient intelligence to receive mentoring from the cathedral curate, who supervised his education and brought him to the cloth.

The Oberndorf museum at the old parsonage opposite the Silent Night chapel picks up the story with its exhibits focusing on that Christmas Eve, 1818.

The church organist at the time was Franz Xaver Gruber, a schoolteacher only five years older than Mohr, who worked in the village of Arnsdorf three miles north.

As floodwaters from the Salzach had been regularly inundating Oberndorf -- including the church of St Nicholas -- water damage had left the organ in need of a visit from the tuner.

To provide alternative music, Mohr picked up a poem he'd written and asked Gruber to put it to music for guitar and two voices. Gruber knocked it out in an afternoon.

Franz Gruber was a school teacher in Salzburg -- his classroom is now a visitor attraction. John Malathronas

That evening Mohr sang tenor and played guitar, Gruber sang bass and the congregation sang the chorus of "Silent Night." Because guitar was not an "approved" church instrument, they had to perform the song after Mass.

Silent Night with its mournful melody and message of hope struck a chord among the destitute community of barge workers, coming as it did after the devastation of the Napoleonic Wars and the distressing split with the neighboring town of Laufen.

The salt trade was in decline, anyway -- even Nocken, the giant boulder, had been dynamited by the Salzburg authorities, removing the natural river halt.

"Don't marry a bargeman," ran the local saying. "In the summer you don't have a husband and in the winter you don't have any food."

Sleeper hit

The Silent Night chapel was consecrated in 1937. John Malathronas

But how did an obscure village carol conquer the world?

Enter Karl Mauracher, the organ tuner.

He finally arrived in the New Year, heard the song and returned with the sheet music to his home town of Fügen in Tyrol.

The Tyrolese had a long tradition of choirs who made money during the barren winter months by touring German towns, not unlike the von Trapp family in "The Sound of Music."

Two local groups, the Strasser and the Rainer family singers, heard "Silent Night" and included it in their repertoire. Before long it became widely known in Germany, then Europe and, in 1839 -- as the Rainer family crossed the Atlantic -- the United States.

In 1854 the Prussian Court's Hofkapelle (chapel musical ensemble) wrote a letter to Salzburg asking who composed the song.

Gruber answered the letter, explaining that he wrote the melody and Mohr, by then deceased, the lyrics.

By the 1920s, "Silent Night" was so well known that a chapel was built on the spot where St Nicholas church stood.

Construction started in 1924 but was only consecrated in 1937, disrupted by -- what else -- frequent flooding.

Mohr's grave in Wagrein. John Malathronas

Although Gruber had a portrait painted during his rather successful lifetime, there was no image left of Mohr, who died young.

To create a likeness, a sculptor, Josef Muehlbacher, had Mohr's skull exhumed from his grave in the village of Wagrein, the priest's last posting.

All the portraits we have of him, including those in the Silent Night chapel, are Muehlbacher's imagined impressions.

For whatever reasons, the skull never found its way back to Wagrein, and is interred behind the nativity scene in the Silent Night chapel meaning, somewhat ironically, that his remains have not been left to sleep in heavenly peace.

How to get there

Salzburg can be reached in two hours by train from Vienna.

Oberndorf can be reached by taxi (roughly $25) from Salzburg in 20 minutes.

Details about the museums and tours in Salzburg: www.salzburg.info