During the French occupation, inspections of the river began in 1796, which were to be followed by a comprehensive expansion. Due to political developments, however, this expansion did not take place. The newly created Duchy of Nassau eventually began work from 1808 under the Chief Construction Inspector of Kirn to make the Lahn fully navigable. In the first winter, the section of the riverside from the mouth to Limburg was stabilized, particularly so that the course could be narrowed in shallow places. It was planned in the long run to make the Lahn navigable as far as Marburg and from there to construct a canal to Fulda to connect it with the Weser. This would create a waterway from France to North Sea via the states of the Confederation of the Rhine. Upstream of Limburg, however, the work was slow, partly because the population pressed into emergency service only reluctantly cooperated. Large parts of the shore were only secured with fascines, which rotted shortly thereafter.