During the later half of the 18th century real income dwindled to reach an all-time low in 1810 when it corresponded to roughly half that of the 1730s; public officials being those worst affected. Norrköping became the greatest manufacturing city of Sweden and Gothenburg developed into the key trading port because of its location on the North Sea. Most people still lived within the present Old Town, with a growth along the eastern shore. Population also grew on the surrounding ridges, more so in the wealthy district Norrmalm and less so in the poor district Södermalm. However, many of the ridges surrounding the city were slums mostly rural in character without water and sewage and frequently ravaged by cholera. In the second half of the century, Stockholm regained its leading economic role. New industries emerged, and Stockholm transformed into an important trade and service centre, as well as a key gateway point within Sweden. While steam engines were introduced in Stockholm in 1806 with the Eldkvarn mill, it took until the mid-19th century for industrialization to take off. Two factories, Ludvigsberg and Bolinder, constructed in the 1840s were followed by many others, and the economic development that succeeded resulted in some 800 new buildings being constructed 1850–70 — many of which were located in the Klara district and subsequently demolished in the Redevelopment of Norrmalm 1950–70. During the 1850s and 1860s, gas works, sewage, and running water was introduced. Many streets were paved, including Skeppsbron and Strandvägen, and the railway brought Stockholm closer to continental Europe — an event which additionally lead to the creation of the first suburb Liljeholmen where railway workshops were located. As the railway was extended further north, Stockholm Central Station was inaugurated in 1871. The first horse-pulled trams were introduced in 1877. Long before the railway, steam engines became common on boats which resulted in many summertime residences being built around Stockholm. But the booming urban development was also notable in central Stockholm where several prominent Neo-Renaissance buildings were built, including the Academy of Music and Södra Teatern. In 1866, a commission led by Albert Lindhagen produced a city plan for the ridges ("malmarna") designed to offer citizens light, fresh air and access to Swedish nature by mean of parks and plantations. To this goal, he proposed a system of esplanades culminating in Sveavägen, a 2 km long and 70 m wide boulevard inspired by Champs Elysées. 1877–80 new city plans were finally passed for central Stockholm, which made the city well-prepared for the major expansion that followed.