We are, at present, stuck on it behind a 16-ton lorry that has slid over the edge and now teeters perilously above a vertiginous drop. In our traffic jam are television crews, huge lorries carrying aid, refugees and Croatian soldiers moving to and from the front, and local farmers moving their sheep to winter pastures. All the participants in the Bosnian war are here, patiently waiting for British engineers to turn up and clear the road.
Split is 70km (43 miles) and seven hours behind us. We left there before first light this morning and threaded our way through the ascending ridges that block access to the Dinaric Alps, to arrive here. We are trying to reach the forward British positions another 100km (62 miles) ahead by nightfall.
Along this road and a parallel one like it, already treacherous with ice covered by a thin scud of snow, must pass every round of ammunition, ration of food and spare part to keep our troops operational in the Bosnian winter. It is, I am told, much improved by the Royal Engineers. Goodness knows what it was like before. And goodness knows how they will do it once the real snow comes.
The British military operation in Bosnia is one of the most impressive and professional I have ever seen. Among the 2,500 troops are every arm of the British Army, from the Cheshires at the front line to Royal Corps of Transport drivers, many of them women, who drive huge trucks over these fearsome roads. They are skilled, courageous and totally committed to their task.
The Government may doubt whether the aim of preserving human life and civilised standards of behaviour is worth taking risks for, but not one soldier I have spoken to does.
The British are setting the standards here. And, perhaps more important, they are mapping out, carefully, skilfully, the rules by which this kind of operation, likely to be the chief role of the Western soldier in the future, is conducted.
The question is, what is it all for?
Brilliant though the conduct of our operations in support of the United Nations in Bosnia is, I am still unclear as to what its aim is.
Ask the force commanders this question and they will give you a very clear answer. Their role is to assist in the provision of humanitarian aid. This is fine. But to what long-term political end?
We may be delaying the inevitable in Bosnia. We are certainly relieving the suffering of the beleaguered Muslims in the process. What we are not doing is altering their ultimate fate - extinction.
The military aims may be clear; the political aim is not. The British commanders will tell you that because of their presence, central Bosnia has stabilised, the Bosnian forces are regrouping and the Serbs are being more successfully held back. Maybe, although Sarajevo seems to tell another story. However, if this is happening, it is doing so as a welcome side effect of our actions, not because that is our objective.
The fact is, there is no clearly stated political aim for all this magnificent effort. No one, from the UN downwards, has said clearly that we wish to see a homeland retained for the Bosnian Muslims.
And yet the obliteration of the Muslim community in Bosnia, started by the Serbs and likely to be finished off by the Muslims' present allies, the Croats, would have incalculable consequences for the peace of the region and, perhaps, ultimately the stability of Europe itself.
We simply cannot afford to allow the Muslims to be wiped out here - with the Cheshires and others, bound by their present mandate, standing impotently by and watching it happen. This is a possibility that deeply bothers many of the soldiers whom I have spoken to, and it ought to bother us, too.
Take Sarajevo. The Serbs now have their thumb on the city's jugular, the road along which aid moves from the airport. They are not applying the pressure at present, but they could at any time. And, if they do, shall we, as the Government has been saying, stand idly by while the city and its 300,000 inhabitants fall to the final act of Serbian aggression?
Sarajevo has become a symbol of the UN's will and Europe's capacity to maintain peace around its borders. If, under the eyes of the UN, the city is lost, then with it goes not just lives but the credibility of our actions here today and elsewhere in the future.
Which is why it must not be allowed to happen. And why we cannot allow the superb work of our forces in central Bosnia to be wasted because we cannot or will not define a political aim towards which they can work.
The UN and the international community should now explicitly state that we are not prepared to see the Muslim community swept away. That Sarajevo will not be allowed to fall. That, at the very least, central Bosnia will be preserved as a place where it is possible to be a Muslim and live in peace.
This, of course, would mean redefining the mandate for our troops. It would mean drawing a line on the Serbian advance. It could mean, initially at least, doubling the number of troops in the area and providing them with the resources they need, especially air cover. It would mean, in the long run, embarking on a Cyprus-type operation - possibly even for a number of years.
Risky? Yes. Costly? Certainly. Yet in the end, perhaps less risky and costly than continuing as we are, doing enough to make the conflict more bearable, but too little to stop it; enough to raise hopes, but too little to satisfy them; enough to delay the spread of the conflict, but too little to prevent it.
The soldiers clearing this vicious little track through the snowy woods are performing a job to be proud of. They need an aim to be proud of, too.
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