After the Congress of Vienna of 1814 -- 1815 , Danzig was reincorporated into Prussia .
On 6 December 1807 , under French occupation , the Danzig - Prussian convention made the town part of the Napoleonic Free City of Danzig .
After the Congress of Vienna of 1814 -- 1815 , Free City of Danzig was reincorporated into Prussia .
On 6 December 1807 , under French occupation , the Danzig - Prussian convention made the town part of the Napoleonic Free City of Danzig .