Artabanus IV of Parthia in the context of "Pars (Sasanian province)"

The Sasanian Empire (/səˈsɑːniən/), officially Eranshahr (Middle Persian: 𐭠𐭩𐭥𐭠𐭭𐭱𐭲𐭥𐭩 Ērānšahr, "Empire of the Iranians"), was an Iranian empire that was founded and ruled by the House of Sasan from 224 to 651 AD. Lasting for over four centuries, the length of the Sasanian dynasty's reign over ancient Iran was second only to that of the Arsacid dynasty of Parthia which immediately preceded it.

Founded by Ardashir I, whose rise coincided with the decline of Arsacid influence in the face of both internal and external strife, the House of Sasan was highly determined to restore the legacy of the Achaemenid Empire by expanding and consolidating the dominions of the Iranian nation. Most notably, after defeating Artabanus IV of Parthia at the Battle of Hormozdgan in 224, it began competing far more zealously with the neighbouring Roman Empire than the Arsacids had, thus sparking a new phase of the Roman–Iranian Wars. These efforts by Sasanian rulers ultimately led to the re-establishment of Iran as a major power of late antiquity.

The Parthian war of Caracalla was an unsuccessful campaign by the Roman Empire under Caracalla against the Parthian Empire in 216–17 AD. It was the climax of a four-year period, starting in 213, when Caracalla pursued a lengthy campaign in central and eastern Europe and the Near East. After intervening to overthrow rulers in client kingdoms adjoining Parthia, he invaded in 216 using an abortive wedding proposal to the Parthian king Artabanus's daughter as a casus belli. His forces carried out a campaign of massacres in the northern regions of the Parthian Empire before withdrawing to Asia Minor, where he was assassinated in April 217. The war was ended the following year after Parthian victory at the Battle of Nisibis, with the Romans paying a huge sum of war reparations to the Parthians.

Ardashir I (Middle Persian: 𐭠𐭥𐭲𐭧𐭱𐭲𐭥, romanized: Arda(x)šēr), also known as Ardashir the Unifier (180–242 AD), was the founder of the Sasanian Empire, the last empire of ancient Iran. After defeating the last Parthian shahanshah Artabanus IV on the Hormozdgan plain in 224, he overthrew the Arsacid dynasty and established the Sasanian dynasty. Afterwards, Ardashir called himself shahanshah and began conquering the land that he called Eranshahr, the realm of the Iranians.

There are various historical reports about Ardashir's lineage and ancestry. According to al-Tabari's History of the Prophets and Kings, Ardashir was son of Papak, son of Sasan. Another narrative recorded in Kar-Namag i Ardashir i Pabagan and Ferdowsi's Shahnameh states that Ardashir was born from the marriage of Sasan, a descendant of Darius III, with the daughter of Papak, a local governor in Pars.

The Parthian, or Arsacid, monarchs were the rulers of Iran from their victories against the Hellenistic Seleucid Empire in the 140s BC (although they had ruled a smaller kingdom in the region of Parthia for roughly a century at that point, founded by Arsaces I) until the defeat of the last Parthian king, Artabanus IV, at the Battle of Hormozdgan in AD 224. At the height of their power, the Parthian kings ruled an empire stretching from present-day central-eastern Turkey to present-day Afghanistan and western Pakistan.