Berlin is a city that has gone through many changes in its history. It has developed from a small settlement on the banks of the Spree into one of the most important metropolises in Europe. Over the centuries, Berlin has mastered many political, economic and cultural challenges. The history of Berlin begins in the 13th century, when the Margraves of Brandenburg built a castle on the Spree. This castle was the origin of the city of Berlin. In the 15th century, Berlin became the residence of the Electors of Brandenburg. In the 17th century, Berlin became the capital of the Kingdom of Prussia, which later became part of the German Empire. In the second half of the 19th century, Berlin developed into an important industrial city. Factories and residential areas emerged, which allowed the city to grow rapidly.