The history of Copenhagen dates back to the first settlement at the site in the 11th century. From the middle of the 12th century it grew in importance after coming into the possession of Bishop Absalon, and the city was fortified with a stone wall during the 13th century. The harbour and the excellent possibilities for herring fishing contributed to Copenhagen's growth and development into an important trading centre. It was repeatedly attacked by the Hanseatic League as the Germans became aware of its expansion. In 1254, it received its charter as a city under Bishop Jakob Erlandsen.
The town was significantly enlarged under Christian IV of Denmark after his coronation in 1596 by the addition of new city districts and modern fortifications with earthworks and bastions. The king commissioned German and Dutch architects and craftsmen to construct magnificent edifices designed to enhance his prestige. By the time of Christian IV's death in 1648, Copenhagen had become Denmark's principal fortification and naval port, and the town formed a framework for the administration of the Danish kingdom and as a centre of trade in Northern Europe.
During 1658-59 it withstood a severe siege by the Swedes under Charles X and successfully repelled a major assault. In 1728 and again in 1795, the city was ravaged by large fires, which destroyed most of the medieval part of town. In 1801, a British fleet under Admiral Parker fought a major battle, the Battle of Copenhagen, with the Danish navy in Copenhagen harbour. It was during this battle Lord Nelson famously "put the telescope to the blind eye" in order not to see Admiral Parker's signal to cease fire. When a British expeditionary force bombarded Copenhagen in 1807, to gain control of the Danish navy, the city suffered great damage and hundreds of people were killed. The main reason for the extensive devastation was that Copenhagen relied on an old defence line rendered virtually useless by the increase in shooting range available to the British. But not until the 1850s were the ramparts of the city opened to allow new housing to be built around the lakes which bordered the old defence system to the west. This dramatic increase of space was long overdue, not only because the old ramparts were out of date as a defence system, but also because of bad sanitation in the old city. Before this relaxation, the historic centre of Copenhagen was inhabited by approximately 125,000 people, peaking in the census of 1870 (140,000); today the figure is around 25,000. In 1901, Copenhagen expanded further, incorporating communities with 40,000 people, and in the process making Frederiksberg an enclave within Copenhagen.
Since the summer 2000, the cities of Copenhagen and Malmö have been connected by a toll bridge/tunnel (Øresund Bridge) for both rail and road traffic. As a result, Copenhagen has become the centre of a larger metropolitan area which spans both nations. The construction of the bridge has led to a large number of changes to the public transportation system and the extensive redevelopment of Amager, south of the main city.