The province of Tabaristan bordered the south coast of the Caspian Sea. After the conquest of Rayy, Tabaristan was exposed to Muslim attack. From Rayy, Nuaim b. Muqarrin sent an expedition to Tabaristan led by his brother Suwaid bin Muqarrin.
Suwaid proceeded to Qumas. It was a large town in Tabaristan. The people did not choose to fight. On the approach of the Muslim force they opened their gates to them, and surrendered on the usual term of the payment of Jizya, Qumas then fell to to the Muslims without a blow.
From Qumas the Muslim forces proceeded to Jurjan. lt was an important town on the main highway to Merv. The Persian forces under the command of Rozban offered a feeble resistance, but considering further resistance useless asked for terms. The usual terms were offered and Rozban entered into a peace pact agreeing to pay Jizya.
From Jurjan, the Muslim forces marched to Dehistan. Realising that Jurjan had already surrendered the people of Dehistan could not have the courage to resist the Muslims. They surrendered and on their accepting the same terms as had been accepted by the people of Jurjan a treaty was drawn and peace was restored.
From Dehistan the Muslim forces marched to Amul. The Persian garrison at Amul was led by Siphedar. He was a seasoned warrior. He had prepared for defence. Amul had strong fortifications, and the first reaction of Siphedar was to close the gates of the city against the Muslims. The Muslims invested the city. The siege dragged on for a few days, and the citizens of Amul came to suffer from the shortage of water and provisions. Siphedar soon realised that a fight against the Muslims would be like dashing against a rock. He opened negotiations with the Muslims. The set terms were offered by the Muslims and agreed by the Persians. With the signing of the treaty the whole of Tabaristan came under the ruzerainty of the Muslims.