With a good knowledge of components of rock to be used in making dolmen, ancient Koreans made holes in the rock at regular intervals and drove expansive materials into them to cut off the part they wanted for dolmen.

Though several thousands of years have passed, the dolmens, for the most part, have still preserved their original state. That is because they were made by advanced architectural and mechanical methods.

Dolmens in the Pyongyang area have lids shaped like tortoise shell which needed so much work.

Some of the lids present not only shell but head and tail of tortoise in a vivid way.

They show the refined stone-processing skill and developed formative arts of ancient Koreans as well as their worship of tortoise, a symbol of longevity.

All the facts prove that the ancient Koreans' intellectual faculties such as stone-processing skill, architecture and formative arts were on a high level and they had been applied in their labor and life.