Eretria is the name of a town in Euboea, Greece, which was once an important polis (city) in Ancient Greece in the 6th/5th century BC. The name means “city of the rowers” made up from from Greek erétēs (rower) and the verb eressein/erettein “to row” ultimately derived from PIE root word *h₁reh₁- ~ *h₁erh₁- (to row), probably so named because it had a powerful naval force. Spelled Eritrea, it’s the name of a country in the Horn of Africa (a peninsula in Northeast Africa). The name comes from Ancient Greek eruthra thalassa meaning “red sea”, from eruthros (red) and thalassa (sea) both of which derive from a PIE root word.
The first time I came across this name was on a television series called The Shannara Chronicles, based on a series of books by Terry Brooks. One of the main characters is called Eretria. I thought it was a made up name at first until I finally got around to looking it up.