The ruble is the name of a currency unit in a number of countries in eastern Europe. This one-ruble coin was issued by the Russian Empire in 1771, during the reign of Catherine the Great. It is made of solid copper, weighing just over 1.022 kg (2.25 lb), and was designed to be kept in the imperial treasury as metallic backing for the country's paper-ruble issue. Marginally larger than a standard hockey puck, it is reportedly the largest copper coin ever issued. The coin now forms part of the National Numismatic Collection at the National Museum of American History.Coin design credit: Russian Empire; photographed by the National Numismatic Collection