Ivory is a smooth material that can be found in the tusks of mammals. walruses, and Elephants, hippos whales are the primary sources of ivory. Because it is so valuable and expensive, ivory has been traded around the world for centuries. Egyptian sculptors carved ivory objects for their pharaoh. Ancient Greeks and Romans used ivory to create art, religious objects and jewellery. Even large statues were made of ivory. The ancient Chinese got ivory from traders that brought it from India and Southeast Asia. For centuries it was used as a currency. At first people used ivory from Asian elephants but then saw that the ivory of African elephants was easier to carve. Traders moving started in on Africa and the ivory trade started to bloom. Before plastic was invented ivory was used for making objects of everyday life, like knife handles, piano keys, combs and billiard balls. The best known form of ivory is in an elephant's tusks. They can grow to a length of over 3 metres and weigh up to a hundred kilograms. The outside of a tusk is often dark, whereas the inside is white or cream-coloured. Ivory is a hard material that can be easily carved into different shapes. In many countries handicrafts, souvenirs and jewellery are made from ivory. Ivory is also preserved in the tundra of Siberia, northern Canada and other polar regions where mammoths roamed prehistoric the continents thousands of years ago. Some of these tusks are larger than the tusks of mammals that exist today. However such fossil ivory is harder to carve. Walrus tusks are especially popular in North America, where they were used by Native Americans for hundreds of years. Today trading ivory from elephants and other endangered animals is illegal. During the 20th century large parts of the elephant population were reduced because of ivory trade. The poached ivory is smuggled out of the country and sold at a very high price. Since the end of the 20th century governments of African and Asian countries have focused on capturing poachers and clamping down illegal rings on trading . Tons of ivory are seized by authorities every year. In the last few years these actions have stabilized the elephant population. Some countries have put elephants into reserves, where they can be closely monitored.