The Königsberg fortifications were erected due to the vulnerability during which war of 1563-1721?
Königsberg fortifications: The fortifications of the former East Prussian capital Königsberg (now Kaliningrad) consist of numerous defensive walls, forts, bastions and other structures. Polish–Swedish wars:  Broadly construed, the term refers to a series of wars between 1563 and 1721.
i don't know