Coins have been used as a form of currency across the world for almost three thousand years. Much like today, the earliest coins were formed from metals, with more precious metals reflecting higher monetary value. The most common shape of coin is a flat, rounded disc shape, which also tends to be small in size. Antique and rare coins can hold high value on the collectors' market, and some coins produced by France can be of particular interest to numismatists. For many years, the French franc was the currency of the western European nation, until the introduction of the Euro in 1999. Before the First World War, some francs were produced in gold; some 19th century gold coins are particularly coveted by collectors, as they feature the bust of the French leader, Napoleon. Since the introduction of the Euro, commemorative coins have been issued in France, celebrating the country's people and achievements.