The fortitude of Sarajevo, capital of Bosnia, made it the centrepiece of the Dayton peace accords, signed in December, which established a multi- ethnic state in Bosnia. Under the agreement, Sarajevo is to be the seat of a Bosnian federal government, including all three nationalities. This federal government stands above the Bosnian Serb Republic, which occupies the north and east of the country, and the Muslim-Croat Federation in its south and west.
The significance of Sarajevo extends well beyond Bosnia. It is the linchpin of a policy which embodies the principle that European borders should not be altered by armed aggression, that ethnically cleansed states are unacceptable to liberal democracies.
This week, however, the multi-ethnic culture of Sarajevo that withstood the war is threatened by the peace. Leaders of the Bosnian Serbs are urging their people to abandon five Serbian-dominated districts. These districts were outside the siege, but on Friday they will be reabsorbed by the city when the new federal police begin patrolling. If civilians follow their leaders' advice - and there are signs that an exodus will start once the weather allows - Sarajevo will be left dominated by Muslims and Croats.
The Serbs' departure threatens the Dayton agreement. It would shatter the city's claim - and with it the Bosnian federal government's claim - to being multi-ethnic. The survival of Bosnia as an entity could be jeopardised. Serbia wants to absorb its Bosnian kin and Croatia's long- term ambition is to bring the Croat parts of Bosnia within its borders. Bosnia would be carved up by these two powers, the Muslims would be vulnerable to further persecution and the Western-brokered peace accord would be in tatters.
If this outcome is to be avoided, Bosnian Serb civilians in Sarajevo need reassurance. They are understandably afraid, given their leaders' advice, of retribution, and there is concern among those who fought in the war that they will be arrested. The federal authorities must promise the Serbs that they will be free from persecution and that all ex-combatants, apart from war criminals, will receive an amnesty.
But these measures will not be enough. The guarantors of the Dayton peace settlement - including Britain, France, the United States and Russia - must issue a strongly worded promise that the lives and homes of the Sarajevan Serbs will be safeguarded. It is not too late to save the spirit of Sarajevo, upon which so much else in Bosnia and central Europe depends.