I took our highly energetic older daughter on an expedition to find the Gallo-Roman site of Ambrussum yesterday. It's easy to find coming from Montpellier: exit the A9 at Lunel, pay € 1.30, follow the D34 direction Lunel (South) and take a left on D 110 direction Villetelle. Not shown in Google's streets is that you can bear right and continue parallel to the A9, then turn right again at the next intersection (no explicit sign to Ambrussum) amid vines. Continue past the museum under construction and adjacent excavation to parking at Le Pont. [map]
There's shade for picnicking at the Pont. Constructed around 30 BC, it was used up until the 14th century, then partially dismantled and wrecked by flood waters.
A long-gone embankment (my interpretation) connected this bridge to the nearby section of the Via Domitia.
That's limestone, not the hardest rock in the world, but still those ruts attest to the traffic on this road (view from above here). Uphill are found the remains of fortifications, buildings, a public edifice, and (best of all, in my daughter's opinion) a large patch of wild blackberries.
Taking the same frontage road back to the D34 and A9 entrance, you'll pass a backdoor to an autoroute rest stop ("aire" en français). A stop there to slip through and get ice cream bars from the gas station boutique is highly recommended.