The Pony Express was the first rapid transit and the first fast mail line (the telegraph not being operational here yet) across the North American continent from the Missouri River to the Pacific coast. It was a system by means of which messages were carried swiftly on horseback across the plains and deserts, and over the mountains of the Far West. It brought the Atlantic and Pacific coasts ten days nearer to each other.
The Pony Express actually began as a "publicity stunt", in hopes of winning the million dollar government mail contract for the Central Overland California and Pikes Peak Express Company (COC&PP), and it had a brief existence of only sixteen months before being supplanted by the transcontinental telegraph. Yet it was of the greatest importance in binding the East and West together at a time when overland travel was slow and cumbersome, and when a great national crisis made the rapid communication of news between these sections an imperative necessity.
Pony Express stations were placed at intervals of about 10 miles (16 km) along the route (this is about as far as a horse can go at a gallop). The rider changed to a fresh horse at each station, taking only the mail pouch (called a mochila ) with him. The mochila was thrown over the saddle and held in place by the weight of the rider sitting on it. Each corner had a cantina, or pocket. Bundles of mail were placed in these cantinas. The mochila could hold 20 pounds (10 kg) of mail. Riders were changed about every 100 miles (160 km).
The Pony Express marked the highest development in overland travel prior to the coming of the transcontinental railroad, which it preceded nine years. It, in fact, proved the feasibility of a transcontinental road and demonstrated that such a line could be built and operated continuously the year around - a feat that had always been regarded as impossible.
- Bradley, Glenn D. The Story of the Pony Express: An Account of the Most Remarkable Mail Service Ever in Existence, and Its Place in History. Project Gutenberg Release #4671.