By the second half of the 19th century, Stockholm had regained its leading economic role. New industries emerged and Stockholm was transformed into an important trade and service centre as well as a key gateway point within Sweden. The population also grew dramatically during this time, mainly through immigration. At the end of the 19th century, less than 40% of the residents were Stockholm-born. Settlement began to expand outside the city limits. The 19th century saw the establishment of a number of scientific institutes, including the Karolinska Institutet. The General Art and Industrial Exposition was held in 1897. From 1887 to 1953 the Old Stockholm telephone tower was a landmark; originally built to link phone lines, it became redundant after these were buried, and it was latterly used for advertising.