Baden 9 Kreuzer Error, 1851 Price: €1.31 Million

One of the first stamps issued by the former German state of Baden, it is believed the color error was due to a simple misreading on the part of the printer. The green ink plate was intended to be used for the 6 Kreuzer stamp, but the printer likely simply misread the 9 for a 6, resulting in the fourth most expensive stamp in existence.

The Baden 9 Kreuzer Error became known to collectors in 1894 at the philatelic club of Berlin. In attendance at the meeting was Baron von Türckheim who showed the stamp to his father and discovered that he had two copies of the stamp on letters in his possession! This incredible coincidence accounts for half of the known copies in the world.