 Before the lake Hammarbysjön was transformed into a canal in the 1920s, Skanstull, the southern tollgate of the city, was surrounded by fortifications, including a moat over which a simple wooden bridge led into the city.In 1914, the City Council had determined the double traffic load at Slussen caused by west-east going ships and north-south bound vehicles, would be solved by rerouting the ships south of Södermalm through a canal to be built.Delayed by World War I, the works were finally begun in 1923, and by 1925 a double leaf steel drawbridge was completed, 14.9 metres wide, with a 10.7-metre wide roadway, and a horizontal clearance of 12.5 metres.