06/03/2015 07:35 pm ET Updated Jun 03, 2016

On Top of the Pont du Gard Aqueduct

A lot of things impress you when traveling through the South of France. One of my favorites is the ancient stone aqueduct called the Pont du Gard.

This region is called Provence because it was the first "foreign" conquest as ancient Rome set about to building its vast empire. Since it wasn't Rome proper, they called it "Provincia Romana" (province of Rome) -- and the name stuck.

The Romans left behind some impressive examples of engineering in their first province. The Pont du Gard is one of the most striking, and one of the most visited sights in all of France. And even after many visits, I'm forever impressed by the ability of the ancient Roman engineers. This structure, built with perfectly cut stones fitted together without mortar, was designed to slope ever so slightly -- less than an inch every hundred yards -- as part of a 30-mile canal system that let water flow effortlessly into the city of Nîmes.

The classic view of the aqueduct, from the river, is something every visitor sees. But here's a peek at the actual stream the Romans created -- on the top of that structure. Six times a day, for €4, you can follow a guide (like Michael, who you'll meet in this clip) and actually walk the length of this ancient bridge... an experience you'd miss if you visited without a good guidebook.

Where have you been most impressed by Roman engineering?