Across the Pyrenees, there are a few cross-border tunnels:

– underneath Col de Somport there are two of them: the derelict train-tunnel (in use from 1928 to 1970) and – parallel of it – the modern tunnel of 2003
– underneath Col de Bielsa: the tunnel Aragnouet-Bielsa, opened in 1976
– underneath Col de Perthus: two railway-tubes for the high-speed line Perpignan-Barcelona, opened in 2010.
They all have bordermarkers at the borderline and typically at both sides of the tube. Let’s show what we got.

The somport-tunnel (the new one), these pictures were supplied by Charles Darrieu.
Interesting: the old railway-tunnel should also have bordermarkers, they might resemble the ones in the Bielsa-tunnel. The railway-tunnel is now in use as an emergency-tunnel for the new one.

The Bielsa-tunnel, these pictures were recently found by Jacques Koleck in the Archives of Dax. They are from Jean Sermet himself and are part of a file named “Démarcation frontalière des Hautes Pyrénées – Province de HUESCA” rédigé par Jean SERMET”from 1989 (archive-reference “Jean Sermet  Archives Départementales des Hautes Pyrénées – cote F 398”). The installment of the plaques even involved a binational treaty. And see this account of Jean Sermet of the whole process. Charles Darrieu also has pictures of these markers (and the documents).

Finally, the Perthus-tunnel also has got his share of bordermarkers, two for each tube. Serge Poncet retrieved these pictures from the tunnel-company.