The second Persian empire, was founded in the year 224 AD by Ardeshir papakan, who named the empire as Sassanid after the name of his ancestor, Sassan. The Sassanid was a great empire with a wide territory that ruled Iran, Armenia, Iraq and many other countries until 650s when the Arab conquest put an end to Iranian empires.
Ardeshir Papakan defeated Artabanus V, the last Arsacid (Parthian) king, and founded the Sassanid Empire which was a pure Iranian dynasty who knew themselves as the heirs of the Achaemenids and so they removed all Greek influences.
They were very strict Zoroastrians and the king was considered the representative of god on earth as is seen in a great number of Sasanian bas-reliefs in Fars province where the god is giving kind of divine permit to the king by giving him a ring of kingship.
All during the reign of Sassanid, there were continuous wars with Romans, shown in most of Sasanian bas-reliefs. Even three of the roman kings were captured by Shapur I in these wars.
There are many historical sites remaining from the Sasanian period especially in Fars province the most magnificent of which is Ardeshir Palace in Firuzabad and Bishapur city in Kazerun.
The language and the script of the Sassanids was Sassanid Pahlavi (middle Persian) and the art of the Sassanids has had great influence on Iranian-Islamic art. By Arab conquest of Persia, although the art and culture still survived, the religion which was Zoroastrianism fully declined and most people converted to Islam. Since then, for several centuries Iran was ruled by Arab caliphates and empires.