Prospero Collection on sale in January

The most important collection of ancient Greek coins to come up for sale for the past half century will be sold at auction in New York in January 2012.

The 642 coins - known as the Prospero Collection and estimated to be worth at least 5 million pounds - were collected by an anonymous classical coin enthusiast from the 1960s to the 1990s. They include dozens of rare and unique examples of ancient Greek gold and silver currency in circulations from the sixth to third centuries BC.

A piece of history in your pocket

Having a huge collection of old coins takes time to complete. Hard to find, and the rarity of the coin are the factors why coin collecting is considered one of the most valuable collecting of all time.

It is the simple fact that old coins were often made from precious metals, such as gold or silver. Old coins can often be worth more melted down than they would if they were spent like regular change. However, the fact that they are still stamped coins makes them even more valuable. And their value is only enhanced even more by the fact that they have been around for a while.

If the old coin is rare its value is much higher. The fact that coins are old tends to make them rarer. The older a coin is, the more likely that people have exchanged it for more modern currency and the more likely that the government has gotten a hold of it and melted it down. In fact, most governments have specific legal requirements to destroy old coins in order to keep the money supply modern, making it more difficult for coin collectors to find old coins.