Kala Wewa, Sri Lanka

Kala Wewa is one of the magnificent reservoirs of the ancient world. This reservoir has a circumference of 40 miles and has a total area of seven square miles at full capacity. The ancient spill (pitawana) is measured to be 216 feet in width and 170 ft in length. For comparison, the width of the spill is more than three quarters length of a soccer field! The spill was built using hammered Granite, a solid structure one could imagine. Each block of Granite is shaped precisely to fit its neighbor. The whole structure eventually acts like one huge rock.

https://us.lakpura.com/pages/kalawewa-national-park