Why was Rennes important to the medieval duchy of Brittany?

Rennes held significant importance to the medieval duchy of Brittany primarily as a center of political power and governance. In the 10th century, the ruler of Brittany established the city as the capital of the duchy. Throughout the Middle Ages, Rennes vied with Nantes for this status, as both cities were central to the sovereignty of the region.123

The city's strategic value was recognized early; for example, Nomenoë, the national hero who secured Brittany's independence from the Carolingians, seized Rennes in the 9th century to consolidate his authority as an independent ruler. Beyond its role as a ducal capital, Rennes remained a vital administrative and political hub, eventually becoming the permanent seat of the Parliament of Brittany in the 16th century.142