The Treaty of Tsarskoye Selo was a territorial and dynastic treaty between the Russian Empire and Denmark-Norway. Signed on 1 June 1773, it transferred control of ducal Schleswig-Holstein to the Danish crown in return for Russian control of the County of Oldenburg and adjacent lands within the Holy Roman Empire. The treaty reduced the fragmentation of Danish territory and led to an alliance between Denmark-Norway and Russia that lasted into the Napoleonic Wars. It also made possible the construction of the Eider Canal, parts of which were later incorporated into the Kiel Canal.