Founded by the Sassanid king Shapur I in the 3rd century AD, Qazvin prospered under the Seljuk rulers, who erected many fine buildings. It had a second, much later burst of prominence when the second Safavid king, Tahmasb I (r 1524–76), transferred the Persian capital here from Tabriz. A great patron of the arts, his ambitious architectural plan for Qazvin proved to be only a dress rehearsal for Esfahan, where his successor, Abbas I, set up court in 1598.
Qazvin is famed for carpets and seedless grapes. The city was once capital of all Iran and has a considerable sprinkling of minor sights, but for most Western travellers its foremost role is as a launch point for excursions to the famous Castles of the Assassins in the marvellous Alamut Valley.