Cromlechs, also known as dolmens or megalithic tombs, are ancient structures made of large standing stones. These structures are often found in Celtic and prehistoric cultures and are believed to have been used as burial sites or religious monuments. While cromlech is the most commonly used term for these structures, there are several other synonyms that are also used. For example, in Wales, they are referred to as "carreg-y-leidr" or "stone thiefs". In Cornwall, they are called "quoits", while in Scotland they are known as "clava cairns". Other synonyms for cromlechs include "standing stones", "stone circles", and "henges".