The city was founded by the Romans (supposedly by Legio VII Gemina) and became the headquarters for that legion and a centre for the sale of gold from local mines.
In 540CE it was conquered by Visigoths, but they left the Christian inhabitants alone. In 717CE the Moors conquered Leon and sought to impose Islam, but by 742 the city was back in Christian hands, of the kingdom of Asturias. The Astrurian kings shifted the seat of government to Leon in 913, abandoning the Atlantic coast for the high plains land of central Spain. They had already absorbed the former Roman province of Galicia (although occasionally independent Galaician kings would set themselves up) and now they sought to expand further. In doing so, the Count of Castile took to himself royal powers and northern Spain became divided between Leon, Castile and Aragon. Eventually (and not without turmoil) Leon and Castile were united and then, as the Muslims were driven from the peninsula, Aragon added too, to make a unified Spanish kingdom.