In the 10th century most of Northern Italy was formally under the rule of the Holy Roman Empire but was in fact divided in a multiplicity of small, autonomous city-states, the medieval communes and maritime republic. The 11th century marked a significant boom in Northern Italy's economy, due to improved trading and agricultural innovations, culture flourished as well with many universities founded, among them the University of Bologna, the oldest university in Europe. The increasing richness of the city-states made them able to defy the traditional feudal supreme power, represented by the German emperors and their local vassals.