The city was originally built on a the River Aare, but outgrew the natural boundaries by the 19th century. A number of bridges have been built to allow the city to expand beyond the Aare.
Bern is built on very uneven ground. There is an elevation difference of several metres between the inner city districts on the Aare (Matte, Marzili) and the higher ones (Kirchenfeld, Länggasse).
Bern has an area, as of 2009, of 51.62 square kilometers (19.93 sq mi). Of this area, 9.79 square kilometers (3.78 sq mi) or 19.0% is used for agricultural purposes, while 17.33 square kilometers (6.69 sq mi) or 33.6% is forested. Of the rest of the land, 23.25 square kilometers (8.98 sq mi) or 45.0% is settled (buildings or roads), 1.06 square kilometers (0.41 sq mi) or 2.1% is either rivers or lakes and 0.16 square kilometers (0.062 sq mi) or 0.3% is unproductive land.[11]
Of the developed, 3.6% consists of industrial buildings, 21.7% housing and other buildings, and 12.6% is devoted to transport infrastructure. Power and water infrastructure as well as other special developed areas made up 1.1% of the city, while another 6.0% consists of parks, green belts and sports fields. 32.8% of the total land area is heavily forested. Of the agricultural land, 14.3% is used for growing crops and 4.0% is designated to be used as pastures. The rivers and streams provide all the water in the municipality.[11]