As early as the 9th and 10th centuries, Viking trade routes stretched from the icy northern seas to the warm waters of the Mediterranean. Haithabu (Hedeby) became a hub for long-distance trade, including between the North and Baltic Seas. Traders coming from the west used the Treene River to reach Hollingstedt, then transported goods overland to Haithabu and Schleswig. From there, they reached the Baltic via the Schlei estuary, east of what is now Kappeln. At the time, no waterway existed that crossed the Schleswig-Holstein ridge.
Starting in the 13th century, there were many proposals to build a shipping route through Jutland or Schleswig-Holstein, but none were realized.
The Stecknitz Canal, completed in 1398, was the first navigable connection between rivers flowing into the North and Baltic Seas. It linked Lübeck and Hamburg, serving inland navigation between these powerful Hanseatic cities.
From 1777 to 1784, under Danish King Christian VII, the Eider Canal was constructed. The history of its planning dates back to 1571. This canal – with its six locks – was the first artificial waterway for seagoing vessels between the North and Baltic Seas. It ran from Rendsburg to Kiel-Holtenau, using the natural course of the Eider River to cross Schleswig-Holstein.
With the rise of steamships, the Eider Canal became outdated. It was too small for increasingly larger ships, and navigating six locks was cumbersome. Moreover, rounding Skagen was now safer with steamships than it had been with sailing vessels.
In the second half of the 19th century, military considerations drove renewed efforts to connect the North Sea with the Baltic via a canal. But it wasn’t until 1878 that Hamburg shipowner Hermann Dahlström was tasked with concrete planning. Starting in 1887, the Kiel Canal (Nord-Ostsee-Kanal) was built over eight years, partially following the old Eider Canal route.