Wikipedia
The Asbarān (singular asbār), also spelled Aswarān, was the name of a military nobility that formed the backbone of the Sasanian army. They primarily composed of Iranian aristocrats from the wuzurgan and the azadan.
They wore mail armor, and ranged from archers to cataphracts. They assumed an description with the bravery, tactics, and ethics of the Sasanians. They mastered in single combat in battles ( mard o-mard), rode on elephants and horses, and their valor was recognized with ornamental emblems. Titles such as hazārmard ("whose strength is equal to one thousand men"), zih asbār ("superior rider"), and pahlawān-i gēhān ("hero/champion of the world"), were their epithets. They wrote the name of the Sasanian emperor and their valuable family members on their arrows as a good omen. They outperformed others in archery to the extent that later writers thought that they had introduced the profession. They were superior and unmatched in the profession, which was even acknowledged by their enemies.
The asbaran have often been demonstrated as an example of existence of feudalism in Iran by modern scholars, who simply refer them as either chevalier, knight, or ritter. According to historians such as Christensen and Widengren, the asbar had the same status as the knight. However, although the asbaran and knight resemble each other in many parts, the economic role and historical role of the knight is very different compared to the role of the asbaran in the Sasanian Empire, which thus makes it incorrect to refer the asbaran as knights.
Most of the asbaran was disbanded after suffering defeat and conquest during the Muslim conquest of Persia. However, several factions of the asbaran, each faction led by a different leader, defected to the Arabs in order to preserve their status and wealth. These asbaran factions settled in various places in the newly established Muslim territories, where they each become known by several names, the most known and prominent faction being the asawira, who under their leader Siyah settled in the newly established settlement of Basra.