The tense, mountainous Georgia-Russia border is monitored by the Organisation for Security and Co-operation (OSCE), whose job it is to observe and record every movement through the mountain passes.
The BBC European affairs correspondent, William Horsley, joined them on their mission.
The OSCE monitors keep a low profile. Their arduous task is to watch 280 kilometres (174 miles) of the Georgia-Russia border.
They do not stop or question travellers. But their sophisticated equipment and teamwork allows them to send back detailed reports about every border crossing, usually with pictures, within 20 minutes.
OSCE monitors record every movement on the porous border
Russia now says it may close the mission down. But at an OSCE ministerial conference in the Bulgarian capital Sofia on Monday other member-states will argue that it is vital for peace in the Caucasus region.
The OSCE monitors are skilled and dedicated people, as I saw during a "hot landing" in the mountains of Georgia, over 3,500 metres up on the border with war-torn Chechnya.
The helicopter came down on virgin snow to put down a team of monitors, carrying cameras, binoculars, thermal imaging gear and satellite phones.
The blades whirred loudly and blew the snow into a blizzard. Avalanches have recently been reported in this area, after heavy snowfalls.
I jumped out with the team leader, Rory Hynes. His group of unarmed monitors, with some Georgian Border Guards and a doctor, would spend the next four hours on that mountain ridge.
"We'll be watching the Ukerigo Pass, which is four kilometres due north," Rory shouted, pointing.
I was glad to get back out of the cold into the helicopter. As it soared back into the sky I saw the snow-covered Ukerigo pass, a majestic dip in the high Caucasus mountains and a favourite crossing-point, when weather permits, between people on both sides.
In winter, the monitors do the job with only 65 people, using Patrol Bases strung along the border, as well as air monitoring, foot patrols, and day and night observation from the exposed mountain peaks.
Many local villagers go down into the valleys and only the hardy venture into the icy mountain passes.
Rory Hynes, from Ireland, is the Patrol Base leader at Girevi, close to the Chechen border.
"Our mission is purely to observe movements across the border in either direction," he says. "If we see pack animals we mention it in the report, including how much they are carrying, and the direction they are going."
It is sensitive work. The monitors are careful not to get drawn into the battle of words that sometimes breaks out between the Russian and Georgian governments. Their information goes at once to all 55 governments of the OSCE member states, including Russia.
Monitors and William Horsley prepare for a "hot landing"
Roy Reeve, the British diplomat who heads the OSCE Mission in Georgia, says his multinational team is fulfilling its mandate well.
"The fact that we do not see large numbers of fighters crossing that border in either direction is confidence-building," he says.
Russian monitors work closely alongside those from over 30 other nations in Europe, Central Asia and North America - and the Border Monitoring Operation has a Russian as its Chief of Operations.
But two years ago the monitors witnessed Russian air strikes on what they claimed were Chechen bandit hideouts in the Pankisi Gorge, close to the border inside Georgia.
Thousands of refugees had fled there during the fighting in the second Chechen war, and the Georgian army needed intensive training from the Americans to drive out armed Chechen rebels among them.
The OSCE mission started in 1999 as a way of defusing those border tensions.
But the monitoring mission faces a new threat during the annual OSCE conference in Sofia on 6-7 December.
Within the past week Russian counter-terrorism officials have again alleged that 300 Chechen and other Islamic fighters have again taken refuge in the Pankisi Gorge.
Those claims are not borne out by the reports of the OSCE monitors.
But Russia has accused the OSCE of being biased and ineffective, and threatened to close down the border mission.
Russia 'part of solution'
Georgia's Foreign Minister Salome Zourabishvili says extending the mandate of the OSCE mission beyond this year is important for the region's stability.
And she says it would be contradictory for Russia to cut the mission at a time when fear of terrorism is high.
The border is only about 50 kilometres from Beslan, where the school massacre of Russian children took place last September.
Some reports say that those responsible reached Beslan across Russia's southern border, from areas outside the scope of the international monitors or the Georgian authorities.
Ambassador Reeve is adamant that Russia must be part of the solution to the various ongoing tensions - both the border monitoring and the chronic problems in the breakaway regions of South Ossetia and Abkhazia, which border Russia.
What happens at the OSCE meeting will be a sign of Russia's intentions towards its "near abroad".