Before the introduction of silk production (date unknown but a pillar of the economy by the 15th century AD), Gilan was a poor province. There were no permanent trade routes linking Gilan to Persia. There was a small trade in smoked fish and wood products. It seems that the city of Qazvin was initially a fortress-town against marauding bands of Deylamites, another sign that the economy of the province did not produce enough on its own to support its population. This changed with the introduction of the silk worm in the late Middle Ages.