Letter writing has a long history dating back to 500 BC. Kings, governments, and militaries were among the first to use letters as a means of communication. Couriers would deliver letters by running long distances or using relay systems with horses. Common writing materials evolved from leaves and tree bark to papyrus to parchment and paper. The first sealed and handwritten letter was sent by a Persian queen in 500 BC. Modern postal systems developed in the 19th century with prepaid stamps allowing universal delivery of letters.