Usually consisting of two or more upright megaliths supporting a large horizontal capstone or ‘table’. Dating from the neolithic period. A dolmen is a type of megalithic structure. Dolmens are ancient monuments and are often associated with burial sites, though their exact purpose and cultural significance can vary from one location to another.

Key features include:
Upright Stones: typically consisting of two or more large vertical stones. Or, orthostats. Placed upright in the ground. These stones may be positioned either vertically or at an angle. Depending on the specific stone, and design.
Capstone: The upright stones support a horizontal stone slab, known as the capstone or table. Its usually flat.
Burial Chambers: During ancient times. Many were used as burial chambers. The capstone would cover a chamber beneath it. And, inside would usually contain remained of the deceased. And/or, burial offerings.
Alignment: Some are associated with astronomical phenomena. Such as the rising or setting of the sun or moon. And at specific times of the year. In addition to burial function. Some had ceremonial and calendrical purposes. In addition to burial function.

Most dolmens date from the Late Neolithic period (4000–3000 BCE)
Some were covered with earth or smaller stones to form a tumulus. Or, burial mound. Thousands of years ago. They used whatever they could. Smaller stones may have been wedged between. Achieving the cap and supporting stones a flatter, or level appearance. Sometimes. The covering had eroded away. Leaving only the stones.

Korea is home to the largest concentration of dolmens
Approximately 40% of the global total are found in the region. An estimated 35,000.

The history is somewhat unknown
The oldest known dolmens are found in western Europe. From around 7000 years ago. Though it is challenging to date. Most of the dating id done from artifacts, or items found in, or close to the dolmens. Since the carbon dating cannot exactly be placed on the supporting or cap stones. It is impossible to prove exactly when many of the stones were set in place.

Types
Great dolmen – Type of dolmen in Nordic megalith architecture
Inuksuk – Inuit built stone landmark or cairn
Polygonal dolmen – Type of dolmen with five to nine supporting stones
Rectangular dolmen – Rectangular, enlarged or extended dolmen
Simple dolmen – Early form of dolmen or megalithic tomb

Origin of the term
Using the spelling dolmin. Théophile Corret de la Tour d’Auvergne (the first bomber of France) described megalithic tombs. In his book Origines gauloises (1796). The current spelling, was more common about a decade after. The name supposedly from Breton. Meaning ‘stone table’. In english, the Oxford dictionary does not use the term. Until a book on Brittany is introduced around 1859.
From 1754 Cornish antiquities though. There is debate. The term in Cornish language for cromlech is tolmen, or ‘hole of stone’. Because of which. There is an argument that Latour d’Auvergne may have just mispelled tolmen. When describing a cromlech. What did you think?

Dolmens are found all over the world, including Europe, Asia, and Africa. Other places too. They are constructed by different ancient cultures. Mostly from the Neolithic period. But also, the bronze age and others. The specific design significance plays an important role. In understanding archaeology and history. And, the artifacts. Are critical to ancient societies, their burials; community practices and success.

Bibliography: “Dolmen” ” (https://www.britannica.com/topic/dolmen). Encyclopedia Britannica.

Corret de la Tour d’Auvergne, Origines gauloises. Celles des plus anciens peuples de l’Europe puisées dans leur vraie source ou recherche sur la langue, l’origine et les antiquités des Celto-bretons de l’Armorique, pour servir à l’histoire ancienne et moderne
de ce peuple et à celle des Français (https://books.google.com/books?id=vmpAAAAAcAAJ&pg=PAPR1), p. PR1, at Google
Books, 1796–97

“Dolmens of Ancient Korea” ” (https://www.worldhistory.org/article/987/dolmens-of-ancient-korea/).

Murphy, Cornelius (1997). The Prehistoric Archaeology of the Beara Peninsula, Co. Cork. Department of Archaeology, University College Cork.