Was the 18th century a time period of gradual market integration? Or did the wars, famines, and criminality drive central European markets away from each other? We perform cointegration tests between four German and three Polish cities for rye markets in the 18th century, plus selected tests with other grains. We confirm earlier findings that Gdañsk was very well-connected. In a dynamic analysis between the early and the late 18th century we find that integration decreased considerably between German and Polish cities. At the same time Polish grain markets appear to disintegrate as well.