Marathon

The long race is named for a plain in Attica.

The modern race commemorates the run associated with the Battle of Marathon in 490 BCE. The place-name became the word for the distance, then for any grind that feels that long.

Every telethon and hackathon is a misreading of a Greek battlefield.

The 1896 Olympic marathon was named for the run from Marathon to Athens with news of the Greek victory over Persia in 490 BC. English speakers then split the word in the wrong place, taking mar-athon as mara plus thon, and the loose ending began attaching to anything long: walkathon in the 1930s, telethon in 1949, hackathon in the 1990s.