The Dissignac tumulus, also known as Bosse de la Prière, discovered in 1873, is a burial mound located five kilometers west of Saint-Nazaire in the Loire-Atlantique department of France.
The Dissignac tumulus covers two dolmens with parallel passages, each eleven meters long. In France, the term “dolmen” is used as a generic name for megalithic structures of all kinds. The three-meter-high tumulus was excavated by J. L’Helgouach in the 1970s, revealing two construction phases. Around 4500 BCE, two dolmens, among the earliest megalithic structures, were erected side by side. Their passages were aligned with the winter solstice. In a second phase, around 3000 BCE, these passages were extended, and the original stone facade was secured by stone walls, giving the tumulus its current stepped structure with a diameter of 28 meters. Rich ceramic findings inside indicate that the site was in use from the older to the younger Neolithic period (between 4500 and 2500 BCE).