In 220 BC, Celtiberian Salamanca was besieged by Hannibal. Later, under Roman rule, it was an important staging post on the Ruta de la Plata (Silver Route) from the mines in Asturias to Andalucía. After the Muslim invasion of Spain, the city repeatedly changed hands. The greatest turning point was the founding of the university in 1218, which grew to became the equal of Oxford and Bologna. The city followed the rest of Castilla into decline in the 17th century, although by the time Spanish literary hero Miguel de Unamuno became rector at the university in 1900, Salamanca had essentially recovered. Throughout the 20th century, especially during the Civil War, Salamanca's university became both the centre for liberal resistance to fascism and the object of Franco's efforts to impose a compliant academic philosophy at Spain's most prestigious university. To a small degree, that liberal/conservative tension still defines the character of the town.