Parthian Empire
The Parthian Empire also known as the Arsacid Empire (Modern Persian
Persian language
Persian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan, Tajikistan and countries which historically came under Persian influence...

: اشکانیان Ashkāniān), was a major Iranian
Iranian peoples
The Iranian peoples are an Indo-European ethnic-linguistic group, consisting of the speakers of Iranian languages, a major branch of the Indo-European language family, as such forming a branch of Indo-European-speaking peoples...

 political and cultural power in ancient Persia. Its latter name comes from Arsaces I of Parthia
Arsaces I of Parthia
Arsaces I was the founder of the Arsacid dynasty, and after whom all 30+ monarchs of the Arsacid empire officially named themselves. A celebrated descent from antiquity begins with Arsaces.A 1st century AD tradition casts Arsaces as descending from the 5th-century BC Achaemenid monarch...

 who, as leader of the Parni
The Parni or Aparni were an east Iranian people of the Ochus River valley, southeast of the Caspian Sea...

 tribe, founded it in the mid-3rd century BC when he conquered the Parthia
Parthia is a region of north-eastern Iran, best known for having been the political and cultural base of the Arsacid dynasty, rulers of the Parthian Empire....

 region in Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

's northeast, then a satrapy (province) in rebellion against the Seleucid Empire
Seleucid Empire
The Seleucid Empire was a Greek-Macedonian state that was created out of the eastern conquests of Alexander the Great. At the height of its power, it included central Anatolia, the Levant, Mesopotamia, Persia, today's Turkmenistan, Pamir and parts of Pakistan.The Seleucid Empire was a major centre...

. Mithridates I of Parthia
Mithridates I of Parthia
Mithridates or Mithradates I was the "Great King" of Parthia from ca. 171 BC - 138 BC, succeeding his brother Phraates I. His father was King Phriapatius of Parthia, who died ca. 176 BC). Mithridates I made Parthia into a major political power by expanding the empire to the east, south, and west...

 (r. c. 171–138 BC) greatly expanded the empire by seizing Media
The MedesThe Medes...

 and Mesopotamia
Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...

 from the Seleucids.