The Köpet Dag, Kopet Dagh, or Koppeh Dagh (; ), also known as the Turkmen-Khorasan Mountain Range, is a mountain range on the border between Turkmenistan and Iran that extends about along the border southeast of the Caspian Sea, stretching northwest-southeast from near the Caspian Sea in the northwest to the Harirud River in the southeast. In the southwest it borders on the parallel eastern endings of the Alborz mountains being together part of the much larger Alpide belt. The highest peak of the range in Turkmenistan is the Mount Rizeh (Kuh-e Rizeh), located at the southwest of the capital Ashgabat and stands at . The highest Iranian summit is Mount Quchan (Kuh-e Quchan) with . Etymology Vambery conjectured that köpet originates from the Turkmen language where "köp" means "a lot" or "many" and the word "dag" means "mountain" or "peak". He thus translated Köpetdag as "Many mountains (peaks)". He and others noted that in Persian koppeh means "pile" or "heap", and the word dag or dagh means "mountain" in Turkic. Thus, a second conjecture held that the Persian version of Kopet Dagh or Koppeh Dagh could be defined as "the mountain that is piled or heaped" and therefore the words could mean "piled or hilly mountains" or "low hills" in general. Ataniyazov, however, rejects those hypotheses:The word kopet is probably derived from the Persian word kuhibet (kuh - "dag", bet - "bad") and means "bad mountain". No name was given to the entirety of this range, but a name was given to each part of it...According to Murzayev, the section of this mountain range west of Ashgabat was called Kopetdag (Murzayev. SA, p. 248). The most common name for this part of the range was Taňrigargan ("God bless you")...the Persians called it Kupet...(in Persian this name is wah, i.e., it is spelled with a long drawn-out Ku: pet and Ku: bet). For the most part, it was very dangerous to cross, because of the wind and the cold. That is why the Persians call the mountain range "bad mountain" and the Turkmens call it "God bless you". In the second half of the last century, Russian scholars who studied in the Kopetdag passed the name onto maps as the name of the entire range and spread it to the public. Many of the elders living in the foothills of the Kopetdag do not know the name Kopetdag...Vambery conjectures that