The Carnac stones are a collection of megalithic sites located in Brittany, France. They consist of over 3,000 standing stones, known as menhirs, arranged in various alignments and formations. These stones date back to the Neolithic period, around 4500 BC, and are believed to have been used for ceremonial or astronomical purposes. The largest group of stones is found in the Alignments of Carnac, where rows of menhirs stretch for over a mile. The exact purpose of the Carnac stones remains a mystery, but they are thought to be connected to ancient rituals or possibly serve as markers for celestial events.