2. Pont du Gard
The precision of Roman engineers never ceases to amaze: Pont du Gard is just one section of what once was a 50-kilometre aqueduct that channelled water from a spring at Uzès to the city of Nîmes.
All that way, weaving through the mountains and travelling underground, there’s just a 17-metre change in elevation.
The outstanding fragment remaining is Pont du Gard, where it crosses the Gardon River, and has a minute 2.5-centimetre gradient.
This bridge is nearly 50 metres in height, with three tiers of arches.
It’s a UNESCO site and one of Roman France’s most treasures landmarks.