The old Latin-based language Romansh, which has survived for hundreds of years deep within Graubünden's isolated valleys, is becoming increasingly marginal.
Changes in society and, above all, the increasing use of German have led to a marked drop in the number of Romansh speakers.
Romansh is now spoken by 0.5 per cent of the Swiss population – or around 35,000 people - compared with 1.1 per cent in 1910.
And within the southeastern canton of Graubünden, the Romansh heartland has contracted significantly. It is now concentrated in Lower Engadine and in Surselva, although pockets exist in other places.
One main reason for the decline is the changing economy. The advent of tourism and industry in Graubünden has led to an intermingling of cultures and the need to speak other languages.
The old rural ways of life, in which Romansh is firmly rooted, are slowly dying out.
"Romansh is becoming more spoken in family and social contexts," Constantin Pitsch from the Federal Culture Office's language services, told swissinfo.
"It is no longer used very much in the fields of economy and administration and this automatically makes Romansh a spoken language and not a written one."
Pitsch is himself a Romansh speaker, but left his homeland in Val Müstair to work in the Swiss capital, Bern. He is not alone, as an estimated 38 per cent of native Romansh speakers live outside Graubünden.
According to Anton Killias, a leading member of the largest Romansh expat community in German-speaking Zurich, this is because of the lack of prospects at home.
"Zurich is the biggest Swiss economic metropolis, so it's very attractive. To go to university you have to go away and Zurich is the closest. Many simply stayed afterwards," he told swissinfo.
Another factor in the language's decline is the lack of a single Romansh identity. There are five Romansh idioms in Graubünden, most of which are quite different from each other.
There is no linguistic centre for Romansh, as the cantonal capital, Chur has been German-speaking since the 16th century.
The community therefore remains fragmented and tends to resist any "pan-Romansh" projects, such as the unified language, Rumantsch Grischun.
But perhaps the biggest threat to Romansh comes from German, which has made huge inroads into Graubünden over the past 50 years at a cost to the canton's other two official languages.
In 1950, 56 per cent of the population spoke German, 29 per cent Romansh and 13 per cent Italian.
In the 2000 census, the figures stood at 68 per cent for German, 15 per cent for Romansh and ten per cent for Italian.
German speakers mainly come to the Romansh heartland for work or family reasons. An estimated 50 per cent of spouses are not native speakers of Romansh.
"A lot of mixed families speak German and as soon as the families don't speak the local language anymore the whole area is under threat of being Germanised," said Andrea Rassel from Lia Rumantscha, the Romansh promotion organisation.
Romansh speakers are nowadays bilingual in German, which they often use at work or as a source of news and information.
This causes problems when it comes to choosing between the two. In the last Swiss census only around 35,000 people said Romansh was their "strongest" written and spoken language.
For Bernard Cathomas, the head of the public service Radio and Television Romansh (RTR), which serves the small community, the wording of the question explains why the number was so low. It simply didn't take into account when Romansh was spoken, such as away from work.
"In fact, there are more than 100,000 Romansh speakers in Switzerland, a number you never hear about," he told swissinfo.
Efforts are being made by the authorities in Switzerland to preserve Romansh and laws exist to protect it. The Swiss Broadcasting Corporation – swissinfo's parent company – recently opened a new media centre in Chur.
But although Cathomas and Rassel say they have noticed a renewed interest in the language over the past few years, especially among young people, it is still a statistical probability that Romansh could die out within a few decades.
"It might happen, you never know. It really depends whether we can make the turnaround," said Rassel.
"As soon as you have the population being absolutely sure they want to speak Romansh, they will make an effort. If this doesn't happen then it won't work."
swissinfo, Isobel Leybold-Johnson in Bern and Chur
0.5 % of the Swiss population speak Romansh.
It is the 11th most commonly spoken language in Switzerland.
There are more speakers of Serbian, English and Turkish in Switzerland than Romansh.
15% people speak Romansh in Graubünden, 10% Italian and 68% German.
The percentage of Romansh speakers in the canton has fallen by a half over the past 50 years.
This year's autumn parliamentary session is taking place in Romansh-speaking Flims, in the southeastern canton of Graubünden, from September 18-October 6.
As well as an influx of members of the political, economics and cultural sectors, the region of Surselva around Flims is also expecting an increase in visitors.
To mark the event, swissinfo is publishing a series of articles and a dossier on Romansh, delving into the past present and future of Switzerland's threatened fourth national language.