Arcathius (Greek: ο Άρκαθίας means in Greek ruler, flourished second half of 2nd century BC and first half of 1st century BC) was a Prince from the Kingdom of Pontus. He was a prince of Persian and Greek Macedonian ancestry. Arcathius was among the sons born to King Mithridates VI of Pontus and his sister-wife Laodice. He was born and raised in the Kingdom of Pontus.
Arcathius joined his father’s generals Neoptolemus and Archelaus with 10,000 horses which he brought from Lesser Armenia at the commencement of the First Mithridatic War (89 BC–85 BC). He participated in the great battle fought near the Amnias River in Paphlagonia which King Nicomedes IV of Bithynia was defeated.
He was a brilliant cavalry commander. In 86 BC, Arcathius invaded Macedonia with a separate army and completely conquered the country. He then proceeded to march against the Roman Dictator Lucius Cornelius Sulla, but on his way, Arcathius died near Mount Tisaion. Arcathius was a happy person in character and his father considered him as a beloved son and as a victorious hero in war.