The Battle of Nahāvand is fought in 642 between Arab Muslims and Sassanid armies.

The battle is known to Muslims as the "Victory of Victories."

The History of Tabari mentions that Piruzan, the officer serving the Persian King Yazdgerd III had about 100,000 men, versus a Muslim army of about 30,000-100,000.

The Persians were outmaneuvered, trapped in a narrow mountain valley, and lost many men in the ensuing rout.

Yazdegerd escapes to the Merv area, but is unable to raise another substantial army.

It is a decisive victory for the Rashidun Caliphate and the Persians consequently lose the surrounding cities including Sephahan (renamed Isfahan).

The Khan of the Turks later lends him some soldiers, but the soldiers mutiny in the year 652.The former Sassanid provinces, in alliance with Parthian and White Hun nobles, resist for a few more years in the region south of the Caspian Sea, even as the Rashidun Caliphate is replaced by the Umayyads, thus perpetuating the Sassanid court styles, Zoroastrian religion, and Persian speech.