The Third Indo-Sassanid Empire was an Indian empire, holding dominion over much of the northern half of the subcontinent, that was ruled by a branch of the Sassanid Dynasty from Persia. It was founded in 665 by Firuz Nirvasita, succeeding the Gupta Empire which had collapsed several decades before and the Second Indo-Sassanid Kingdom which occupied parts of Punjab and Gandhara.
Its founder, Firuz Nirvasita, was the son of the deposed emperor of Persia, Yazdegerd III, who fled to India to escape the assassination attempts of the new emperor Shahryar. Growing up in the Gandharan court, he took the opportunity to build his own kingdom from the ruins of Gupta, and by the time he died in 710 he ruled everything from Gandhara to Bengal. His son Narsieh invaded Persia in 718 to claim his grandfather's throne, and the Indian territories were subsequently inherited by Narsieh's second son, Darius I.
Narsieh, in order to gain Roman support for his invasion of Persia, invited the Islamic theologian Malik Dinar to his court and allowed missionaries to roam freely throughout his domains, though he himself stayed faithful to Zoroastrianism and Hinduism. The growing Muslim community thrived under he and his successors and, though it was suppressed by later kingdoms and empires, it is still today a majority in the coastal regions of Sindh and Gujarat.
The Indo-Sassanid empire lasted until the 12th century before entering its final decline. In 1019 Ardashir III was defeated by Rajendra Chola I, who marched all the way to the Ganges before returning to southern India, thus demonstrating to all the weakness of the Indo-Sassanids. After that there was no stopping their decay as local rulers asserted their independence, and the kingdom finally fell in 1174. The Sassanids were succeeded as the dominant power in the region by the Shansabanids.