Euthymenes was a Greek explorer from Massilia (Marseille), who explored the coast of West Africa as far, apparently, as a great river, of which the outflow made the sea at its mouth fresh or brackish. His published accounts have not survived, but seem to have been known, at least at secondhand, by Plutarch

Plutarch

Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...

, who writes "Euthymenes the Massilian concludes that the Nile is filled by Oceanus

Oceanus

Oceanus ; , Ōkeanós) was a pseudo-geographical feature in classical antiquity, believed by the ancient Greeks and Romans to be the world-ocean, an enormous river encircling the world....

 and that sea which is outward from it, the latter being naturally sweet." Euthymenes thought that this river was the Nile

Nile

The Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world. It is long. It runs through the ten countries of Sudan, South Sudan, Burundi, Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Ethiopia, Uganda and Egypt.The Nile has two major...

, but the river in question may have been the Senegal

Sénégal River

The Sénégal River is a long river in West Africa that forms the border between Senegal and Mauritania.The Sénégal's headwaters are the Semefé and Bafing rivers which both originate in Guinea; they form a small part of the Guinean-Malian border before coming together at Bafoulabé in Mali...

. (Branigan 1994)

Seneca the Younger

Seneca the Younger

Lucius Annaeus Seneca was a Roman Stoic philosopher, statesman, dramatist, and in one work humorist, of the Silver Age of Latin literature. He was tutor and later advisor to emperor Nero...

 also knew Euthymenes' account, which he reported in Naturales quaestiones

Naturales quaestiones

Naturales quaestiones is an encyclopedia of the natural world written by Seneca around 65 AD. It is much shorter than the Naturalis Historia produced by Pliny the Elder some ten years later, however.-Content:...

(iv.2.22) and refuted, for various reasons:

"Euthymenes of Massilia says by way of testimony, 'I have navigated' says he, 'the Atlantic sea. Now, the Nile flows, greatly, as long as the Etesian Wind

Etesian

The etesians ', sometimes found in the Latin form etesiae), meltemi μελτέμι , or meltem are the strong, dry north windsof the Aegean Sea, which blow from about mid-May to mid-September...

s endure; for the sea is constantly thrown back by the constant winds; as soon as they have abated and the sea becomes calm, the Nile descends with less force. For the rest, the seawater is fresh to the taste and has wildlife similar to that of the Nile"

The statue of Euthymenes (by Auguste Ottin

Auguste Ottin

Auguste-Louis-Marie Jenks Ottin was a French academic sculptor and recipient of the decoration of the Legion of Honor.-Early life:...

) is featured on the façade of the Marseille bourse.