The Aras River is the Bible’s River Gihon. For millennia its valley formed a major thoroughfare for traders, armies and holy men. Only with the treaties of 1813 and 1828 did Russia and Persia turn it into a border line, and several mud fortifications remain from the 18th-century conflicts that led to its division.

But today the tension is east–west, not north–south. Clearly visible on the Aras’ northern bank are ruined villages, sad signs of the still-unresolved 1989–94 Armenia–Azerbaijan war. What a difference 50m makes: it’s fine to drive along the southern (ie Iranian) riverbank as a casual tourist (though taking photos isn’t advised), but travelling along the parallel northern bank’s now severed train line would be unthinkable folly. That line crosses two globally forgotten front lines: from Nakhchivan (Azerbaijan) to its mortal enemy Armenia, on through Karabagh (Armenian-occupied Azeri territory), and then back through minefields to Azerbaijan again. There’s not been active fighting for over a decade, but the guard posts, bombed-out trains and barricaded tunnels add a considerable geopolitical frisson to the valley’s great natural beauty.