Establishing borders is about sovereignty: but transport infrastructures, and especially railways, are made to cross these borders, and even to cancel them. They also demand countries to share sovereignty over each other territories, in order to build and maintain these infrastructures. The Spanish Archivo Histórico Nacional holds the documents on the construction of the Pau-Canfranc railway, which crosses the Pyrenees to connect France and Spain
This is a complaint initiated by the President of the Zaragoza Provincial Council in 1925, to initiate diplomatic actions in collaboration with the managing commission of the Pau-Canfranc, to resume the works for the railway (which stalled for reasons we can only find out by searching through the documents!)