Around 850, Saint Altfrid founded the "Damenstift", an abbey for women, ruled by a prince abbess. In this time the cathedral of Essen was built. In those days the name of the city was "Assindia" in Latin. Later it changed over "Essendia" and "Essend" to "Essen". 1377 Essen became a "free imperial city". At this time, Essen was just a small city in a region where few people lived. The city became more important when the Industrial Revolution began. In 1811, "Friedrich Krupp" founded a small steel factory in Essen which was fast growing. The city population also grew, and 80 years after the foundation of Krupp's steel work, Essen was a big city with 100,000 inhabitants. Because in the region of the Ruhr River much coal was found, many coal mines were founded in Essen and other near cities. Great industrial families like the "Krupp"s, the "Haniel"s and the "Grillo"s gave money for cultural buildings like the Grillo theatre and the Folkwang museum. Because of its big industry, Essen was destroyed with bombs in the Second World War. Many people gave their lives, and many buildings were destroyed. Not all were rebuilt after WW2. But because the coal mining industry ended mining in Essen in the 1970's (coal from abroad was getting cheaper), the city was getting poor. The "Strukturwandel" (structural change) saved Essen. Old collieries like "Zeche Zollverein" became museums or theatres. In 2003, the universities of Essen and Duisburg joined together as the university Duisburg-Essen.