Rai stones are large, circular stone disks carved out of limestone, with a hole in the middle. Locals in the island of Yap, Micronesia, have used these stones as a form of unusual currency, a "stone money." The size of the stones varies widely; the largest are 3 meters in diameter and weigh 4 metric tons.
The extrinsic (perceived) value of a specific stone is based not only on its size and craftsmanship but also on the history of the stone. If many people - or no one at all - died when the specific stone was transported, or a famous sailor brought it in, the value of the rai stone increases.
Rai stones were used in social transactions such as marriage, inheritance, political deals, sign of an alliance, ransom of the battle dead or just in exchange for food. Many of them are placed in front of meetinghouses or specific pathways. Though the ownership of a particular stone changes, the stone itself is rarely moved.