Lycus or Lykos was an ancient river of Bithynia

Bithynia

Bithynia was an ancient region, kingdom and Roman province in the northwest of Asia Minor, adjoining the Propontis, the Thracian Bosporus and the Euxine .-Description:...

. It flowed in the east of Bithynia in a westerly direction, and emptied itself into the Black Sea

Black Sea

The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

 (Pontus Euxinus) a little to the south of Heraclea Pontica

Heraclea Pontica

Heraclea Pontica , an ancient city on the coast of Bithynia in Asia Minor, at the mouth of the river Lycus. It was founded by the Greek city-state of Megara c.560-558 and was named after Heracles who the Greeks believed entered the underworld at a cave on the adjoining Archerusian promontory .The...

, which was twenty stadia distant from it. The breadth of the river is stated to have been two plethra, and the plain near its mouth bore the name of Campus Lycaeus. (Scylax, p. 34; Orph. Argon. 720; Arrian

Arrian

Lucius Flavius Arrianus 'Xenophon , known in English as Arrian , and Arrian of Nicomedia, was a Roman historian, public servant, a military commander and a philosopher of the 2nd-century Roman period...

, Peripl. p. 14; Anonym. Peripl. p. 3; Xenoph.

Xenophon

Xenophon , son of Gryllus, of the deme Erchia of Athens, also known as Xenophon of Athens, was a Greek historian, soldier, mercenary, philosopher and a contemporary and admirer of Socrates...

 Anab. vi. 2. § 3; Ov. Epist. ex Pont. x. 47; Memnon

Memnon of Heraclea

Memnon of Heraclea was a Greek historical writer, probably a native of Heraclea Pontica. He described the history of that city in a large work, known only through the Excerpta of Photius , and describing especially the various tyrants who had at times ruled Heraclea.Memnon's history encompassed...

, ap. Phot. 51; Plin.

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

vi. 1, who erroneously states that Heraclea was situated on (appositum) the river.)