Standing stones are big rocks that people put upright in the ground a long time ago, like when there were no cars or computers. They are called standing stones because they are standing tall and not lying down like most other rocks.
Some of these stones are very very old, older than any of our grandparents or great-grandparents. People made them in different shapes and sizes, and they used them for different things.
Some people think that standing stones were used to tell time. They could look at the shadow the stone made and tell what time of day it was.
Others think that standing stones were used for special ceremonies or rituals. The people who made them could have used them to honor their gods or ask them for help.
Standing stones can be found all over the world, and some are very famous. Like Stonehenge in England, which has huge stones arranged in a circle, and people still visit it today.