Why did the legend of Pheidippides differ from Herodotus’s account?

The legend of Pheidippides differs from the account provided by the Greek historian Herodotus because the popular story likely conflates the actions of two separate messengers.1

In his History, Herodotus records that Pheidippides was a professional hēmerodromos (day runner) dispatched from Athens to Sparta before the Battle of Marathon to request military aid. This journey covered approximately 150 miles (240 km) over two days. Herodotus makes no mention of a subsequent run from the battlefield to Athens to announce the victory.12

Conversely, the popular legend—later dramatized by poets like Robert Browning—claims that a messenger ran from the battlefield at Marathon to Athens to report the Greek success, dying of exhaustion upon arrival. Historians believe this narrative is a later invention that combined the historical mission to Sparta with a separate, unrecorded run from the battlefield, ultimately inspiring the modern marathon race.12