In September 851, Charles the Bald and Erispoe, a Breton chief, met in the town to sign the Treaty of Angers, which secured Breton independence and fixed the borders of Brittany. However, the situation remained dangerous for Angers, and Charles the Bald created in 853 a wide buffer zone around Brittany comprising parts of Anjou, Touraine, Maine and Sées, which was ruled by Robert the Strong, a great-grandfather of Hugh Capet. In 870, the Viking chief Hastein seized Angers where he settled until a successful siege temporarily displaced him. He again took control of the town in 873, before the Carolingian Emperor ousted him. Fulk I of Anjou, a Carolingian descendant, was the first viscount of Angers (before 898 until 929) and of Tours (898–909), and count of Nantes (909–919). Around 929, he took the title of count (earl) of Angers and founded the first Anjou dynasty, the House of Ingelger ("French: Ingelgeriens"). Angers subsequently formed the capital of the province of Anjou. During the 12th century, after internal divisions in Brittany, the county of Nantes was annexed by Anjou. Henry II Plantagenêt kept it for more than 30 years. The grandson of Henry I of England, he also succeeded to the English crown and ruled the vast Angevin Empire, which stretched from the Pyrenees to Ireland. The castle of Angers was then the seat of the Court and the dynasty. The Empire disappeared in 1204–1205 when the King of France, Philip II, seized Normandy and Anjou. Henceforth there were no more counts of Anjou, as the French king had made Anjou a dukedom. Now a part of the Kingdom of France, Angers became the "Key to the Kingdom" () facing still independent Brittany. In 1228, during Louis IX's minority, Blanche of Castile decided to fortify the city and to rebuild the castle. Later, during the 1350s and 1360s, the schools of Law, Medicine and Theology, renowned in Europe, were organized into a university. In 1373, Louis I of Naples and Anjou ordered the six tapestries illustrating the Apocalypse of St John known today as the "Apocalypse Tapestry". King René of Anjou contributed to the economic revival in a city that had been diminished by the Black Death (1347–1350) and the Hundred Years War (1337–1453).