Spahbed (; early form spahpat, New Persian as Spahbod and Spahbad) is a Middle Persian title meaning "army chief" used chiefly in the Sassanid Empire. Originally there was a single spahbed, called the Eran-spahbed, who functioned as the generalissimo of the Sassanid army. From the time of Khosrau I (r. 531–579) on, the office was split in four, with a spahbed for each of the cardinal directions. After the Muslim conquest of Persia, the spahbed of the East managed to retain his authority over the inaccessible mountainous region of Tabaristan on the southern shore of the Caspian Sea, where the title, often in its Islamic form ispahbadh (; Arabic form isbahbadh), survived as a regnal title until the Mongol conquests of the 13th century.