What was the stone ring built on the wall in ancient times for?

Stone rings built on walls in ancient times have two main purposes.

First of all, stone rings are used to tie animals, such as cows and horses. This is especially common in water towns. People will tie buffaloes to the river with stone rings to facilitate farming.

Secondly, the stone circle can also be used to measure the 24 solar terms. This kind of stone ring is composed of 69 green stone tablets in a special orientation order, which is a kind of lunar calendar. People use the projection of light in the stone ring to judge the 24 solar terms when the sun rises and falls.