Although Duisburg was founded on the River Rhein originally, sometime around the years 1000 to 1200, the Rhein changed course eventually leaving the city 'high and dry'.
This was not strictly true because for about another 400 years, the old course of the Rhein still connected the settlement with the Rhein proper (maybe via the Ruhr at a later date - the nature of the terrain meant that rivers were prone to change course). This old course presumably became incorporated in the Dinkelsbach, which was itself presumably a former tributary (I am a bit vague about the details here). The Dinkelsbach flowed close to the city walls to the south and west from where it eventually entered the Ruhr. However this watercourse itself became silted up over the years.
In 1828-1832 the Rhein Kanal was built to the Marientor area, reconnecting the city to the river again (a harbor was also being developed on the Ruhr further north but at the time this was in Ruhrort, a completely separate town - it only became incorporated into Duisburg in 1905).
The Rhein Kanal (apart from a section which lead off at a right angle adjacent to the Marientor) is the present-day Outer Harbor. In order to increase Duisburg's trade (and independence from the Ruhr harbor), an Inner Harbor was built in 1840 (along a section of the old city walls), its water level being maintained by a lock between the Outer and Inner Harbors.
At the top end of the Inner Harbor, the one-kilometer long Ruhr Kanal was built connecting with the river of the same name.
In 1892, a further extension was added to the top of the Inner Harbor. Most of this top section has now been sectioned off by a dam known as the Portsmouthdamm.
The entire harbor is being developed in a manner reminiscent of similar dockside developments elsewhere
The Inner Harbor was/is bridged by the Schwanentor Bridge (of which several versions have existed).
By the of the 1820s, trade in Duisburg had reached such a volume that the Handlungsvorstand der Kaufleute (the later Chamber of Commerce) proposed in 1826 that a canal should be constructed from the city to the Rhein in order to finally acquire a practical harbor for Duisburg. One factor in their consideration was potential competition from Ruhrort. Simialr plans had been discussed in 1696 and 1796, for example, but were not carried any further. In 1828 however the newly-founded Rheinkanal-Aktienverein began the construction of the present-day Outer Harbor, which was completed in 1832. Thereby an important foundation had been laid for the further economic development of Duisburg in the age of industrialization.
The Bortschiff Concordia was the first to traverse the new canal in 1831. The canal had a length of two kilometers and a depth of between 6,50 to 10,50 meters (the cost was 118,000 talers)
Zum Hochwasserausgleich wurden Rheinkanal und Innenhafen durch eine Sperrschleuse getrennt, der Innenhafen am Schwanentor überbrückt
So Duisburg again had a direct connection by water to both the Rhein and Ruhr and entered into direct competition with Ruhrort. Between 1882 and 1893 the harbor was widened and lengthened. The last harbor to be constructed was the Parallelhafen, completed in 1899, by when the total area of the Duisburg city docks had grown to 51 hectares.
Although initially successful, this success was short-lived as competition arrived from the railways. The railways built their own docks at Hochfeld. In the 1860s, traffic started to decline and 1890 eingestellt, der Ruhrkanal being partly filled in. In 1847, both companies had been combined in the Rhein-Ruhrkanal-Aktienverein.
Initial replacement for declining coal traffic was the timber industry : wood was used for mining, house building, fuel, among others. In 1892, the Inner Harbor was extended eastwards with the Floßhafen. Towards the end of the 1860s, the first grain imports had arrived via Rotterdam. Thye brought companies of the milling industry in their wake.
The construction of the Ruhrort Harbor was initiated in 1820-25 by Ludwig von Vincke, the then president of the Province of Westfalen. Twelve years later construction was begun on the Scheusenhafen which exited into the later Vincke Canal and whose last component is the present-day Bunkerhafen. From 1860-1868, the North and South Harbors were built and simultaneously the Ruhr diverted southwards, in order to obtain better access to the Rhein. Eighteen years, till 1890, was required for the Kaiserhafen, which likewise had direct access to the Rhein, for which a further diverting of the Ruhr was necessary. By now the total area of the Ruhrort docks was 53.3 hectares.
Hochfeld Harbor, south of Duisburg Harbor, formed a third grouping of docks. It consisted of three docks, the North-, South- and Kulturhafen, and was built from 1867-1874 by the Rheinische Eisenbahngesellschaft. i.e the railways. which proved to be a major competitor to the other docks.
With the progressive development of traffic, thoughts turned more and more to uniting all public docks under one body. The great dock building plans of the city of Duisburg and of the state in Ruhrort at the turn of the 20th century would have meant unnecessary competition for both towns, if they had ever come to fruition.
In 1905 the Ruhr executive and the City of Duisburg formed a body for the purpose of the joint administration and utilization of their docks. Simultaneously the three areas of Duisburg, Ruhrort and Meiderich, within whose area all the harbors lay, united to form a single city. The new harbor with three docks A,B, C planned by Ruhrort was temporarily put on hold. For a third time, the Ruhr had to yield to an extension of the harbor and be diverted yet again. The railway-administered docks of Hochfeld and Ruhrort (Eisenbahn Bassin) was brought within the joint arrangement in 1912. Rhein-Herne Canal was opened in 1914 connecting Duisburg with the Dortmund-Ems Cnal at Herne.