The city is supposed to have been the capital of Volga Bulgaria from as early as the 8th century. Regular Russian incursions along the Volga, and internecine fights forced the Volga Bulgarian kings to intermittently move their capital to Bilyar. After a destruction of Bilyar during the Mongol invasion, the older capital became a centre of a separate province (or duchy) within the Golden Horde. During the period of Mongol domination Bolgar acquired immense wealth, many imposing buildings, and grew tenfold in size.