A menhir is a large upright stone that is often found in prehistoric sites across Europe. These stones are typically made of granite or other durable materials and can vary in height and shape. Menhirs are believed to have been erected by ancient cultures for various purposes, including religious rituals, territorial markers, or as part of larger stone structures like megalithic complexes. Many menhirs are associated with the Celtic culture and can be seen in places like Brittany in France and the British Isles. Some menhirs are part of alignments or circles, suggesting they may have had astronomical significance. Today, they are important archaeological sites that attract tourists and researchers alike.