Who used horses and riders to carry letters and packages over great distances?

The Pony Express was a service that used horses and riders to carry letters and packages over great distances in the United States during the mid-19th century. Established in 1860, it significantly improved communication between the East and West coasts, covering about 1,900 miles in approximately ten days. The service was eventually rendered obsolete by the completion of the transcontinental telegraph in 1861.