The Vilaine river, which flows through Vitré and Rennes, borders the territory of Langon over a distance of 14km, then flows on into the Atlantic ocean. Langon one of the best preserved countrysides in all of Brittany.
The city's Roman heritage is evidenced in the Chapelle Ste Agathe, the villa de Balac, and a stretch of paved road. The first Christian communities established themselves in the area starting at the end of the 5th century. The town was built around the chapel.
Starting in the 9th century, the history of the village becomes intertwined with that of the Abbey of Redon. It is in the records of this Abbey that the name of the parish is written using various Latin spellings ("Langedon", "Langeco", "Lanco", and "Lancon").
Langon found itself at the very edge of Britanny, when the Vilaine river became the border between the Breton territory and the French territory.
In the 19th century, the arrival of the railroad through town brought a dynamic economic development and prosperity that had never been experienced. It was during this time that the village took on the look and feel that persists in much of the town to this day. World War II brought an abrupt end to this development.
The chapelle Sainte-Agathe, with a history of 18 centuries, is famous for the Roman paintings on the inside. It was originally built as a Gallo-Roman spa at the end of the 2nd century, then converted to a church in the Middle Ages (6th-7th centuries). It was used as a funerary chapel in the 10th century. To this day, a Roman fresco depicting Venus emerging from the water and surrounded by all sorts of fish has survived.
There are a number of megaliths in Langon and in the surrounding area (particularly in the neighboring town of [St. Just]). One such arrangement has been named the "Demoiselles de Langon", or the "Damsels of Langon". The arrangement consists of around 20 stones, averaging around 1 meter (3 ft) in height.
The Corbinieres viaduct spans the Vilaine river. More than 30 meters high, it links Langon to Messac. It was completed in 1861. The viaduct has distinctive skewed arches. For this reason, it is considered to be one of the most attractive viaducts in France. In addition, its pillars house an important bat colony.