Short answers, pulled from the story.
Parthia is a historical region in northeastern Greater Iran, roughly corresponding to part of northeastern Iran and part of southern Turkmenistan. It was bordered by the Kopet Dag mountain range to the north and the Dasht-e Kavir desert to the south.
The Arsacids were the ruling dynasty of the Parthian Empire, which lasted from 247 BC to 224 AD. They originated from the Parni, an eastern-Iranian people led by Arsaces, who invaded and seized Parthia around 238 BC and made the region the political and military base of their empire.
The Parthian Empire fell in April 224 AD when the Persian Sassanids, a formerly minor vassal from southwestern Iran, defeated the Arsacid dynasty. The Sasanian king Ardashir I is credited with the conquest.
The Parthians spoke Parthian, a northwestern Iranian language. It first appeared on Arsacid coinage during the reign of Vologases I, who ruled from 51 to 58 AD.
Parthian minstrel-poets, called gosans, were present throughout all aspects of daily life, entertaining kings and commoners alike and praising patrons by associating them with mythical heroes. Their oral tradition influenced both Iranian languages and Armenian, and may have continued through the later poetic tradition known as fahlaviyat.
The first indigenous Iranian mention of Parthia is in the Behistun inscription of Darius I, dating to around 520 BC, where it is listed among the governorates near Drangiana. Earlier references appear in 7th century BC Assyrian texts under the name Partakka or Partukka.