The names Kos, Lampedusa, Hegyeshalom may go down in histories of Europe's 2015 refugee crisis yet it is an obscure village in Luxembourg, far from the human drama, that is hogging headlines.
Schengen, on the vine-flanked Moselle where old enemies France and Germany meet, gave its name 30 years ago to the code which removed border controls between most European states. Now, feuding over who should shelter hundreds of thousands of people on the move seeking asylum has put "Schengen" under threat.
The European Commission, the executive of the European Union which enforces the Schengen rules on 26 states including four non-EU members, has ruled out any change. It describes Schengen as one of the greatest achievements of the postwar peace, a boon for citizens and non-European visitors, as well as for business.
"It's not Schengen that's the problem," the commissioner in charge of it, Dimitris Avramopoulos, told Reuters as Budapest, Vienna and Berlin bicker about what to do with thousands of mainly Syrian refugees trying to reach Germany from the Balkans.
The problem, most EU leaders agree, lies less with the lack of internal borders than with the bloc's external frontiers and with another town inscribed in its statutes – Dublin. (With a touch of irony, Ireland, like Britain, shuns the Schengen zone.)
A system first agreed at Dublin in 1990 means that people requesting asylum must be housed and have their claims processed in the state in which they first arrived in the EU. A surge in arrivals by sea has left Italy and Greece struggling. Chaos in Greece means many move on across the Balkans to reach Hungary.
Accepting the Dublin rules must be fixed to spread the load, the Commission proposed to send some asylum-seekers from Italy and Greece around the EU according to quotas based on countries' population, wealth and so on. Bickering has held that up, while Greece and Italy have resorted to DIY methods to relieve the pressure, simply letting migrants head north over their borders.
That has seen France step up checks on traffic around its Italian border, Danes monitoring their German frontier more closely and, this week, Austrian police mounting operations on roads from Hungary. If such procedures are increased and endure, they could undermine Schengen's principles of free transit.
As yet, there appears little appetite among governments to challenge the Commission and undertake the cost and disruption of redeploying frontier police to make routine document checks to intercept the few thousands of migrants, among the millions traveling every day, who are not entitled to move country.
But German Chancellor Angela Merkel, fearful for the open-border system, this week brandished that danger to Schengen as a means to focus minds on agreeing to fix Dublin: "If we don't succeed in fairly distributing refugees," she said, "Then of course the Schengen question will be on the agenda for many."
Former French president Nicolas Sarkozy has been among those who have called for Schengen rules to be abandoned in response to the failure of southern states to defend the external frontier.
Schengen has also come under attack from some who argue that it has made life easier for criminals, including the suspected Moroccan Islamist accused of attacking an international train from Amsterdam via Brussels to Paris last month. However, a call from Belgium for amendments to Schengen made little progress.
The Commission says the Schengen code, which also regulates the sharing of visa data and criminal intelligence, gives states sufficient powers to carry out both security and identity checks where these can be justified. For example, Austria's checks for migrant smugglers were not a problem, EU officials said.
Under rules revised in 2013, Germany reimposed frontier checks as part of its security for the G7 summit in June. Such blanket suspensions of Schengen are normally limited to 30 days.
Were a country to impose routine identity checks at its borders, on roads or at airports and rail stations, it would face legal action by the Commission. In practice though, some fear it could start a snowball effect that the EU might struggle to halt, even if checks might be likely to remain patchy, with governments wary of cost and a public backlash at inconvenience.
"Schengen is under serious stress," one senior European diplomat said, highlighting this week's Austrian action. "If that is permanent, it could spread like wildfire."
Freedom to travel and change residence in the Schengen zone, which includes non-EU members Switzerland and Norway, is not granted to people waiting for asylum claims to be assessed – a process that can take years. They are also supposed to stay in the country that granted them asylum for five years afterwards.
That creates a longer-term difficulty for the asylum system as refugees are tempted to move for work or to join family. Police are supposed to send them back to the EU state where they have residence rights but the system is only patchily applied.
Businesses, particularly in road transport, have raised an alarm about a reimposition of passport checks on truck drivers and others engaged in cross-border activity.
For many political leaders, however, the fate of Schengen is so bound up with the European Union's essential sense of self, as the response to centuries of war between nations, that calls for major change will meet heavy resistance.
Speaking in Schengen in June to mark 30 years of the accord, Avramopoulos said: "On a continent where nations once shed blood to defend their territories, today borders only exist on maps."
In Brussels this week, he raised the alarm about national squabbling over borders undermining the entire project of European integration: "This might be the beginning of the end of all these achievements that we have all made over the last 50 years. That is why Schengen should be defended and protected."