You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "The Königsberg fortifications were erected due to the vulnerability during which war of 1563-1721?" whose answer is The Polish–Swedish Wars.
Each document should contain about 30 words, and these documents should contain useful information.

Query: fortifications in Königsberg during 1563-1721
Useful Output:

Doc 1:  1563 — 1721. Den Kern der vielen und blutigen Kriege, die von der Mitte des Bedeutung des. 16. bis ins 18. Jahrhundert zwischen Dänemark und Schweden geführt
Doc 2: Major fortifications · Astronomic Bastion · Bronsart Fort · Dohna Tower · Friedrich Wilhelm I Fort · Gneisenau Fort · Grolman Bastion · Pillau Citadel · Stein Fort.
Doc 3: 12 The struggle for supremacy in the Baltic between Denmark and Sweden, 1563–1721  fortification which the Dutch had developed during their
Doc 4: The fortifications of Königsberg consist of numerous defensive walls, forts, bastions and other structures. They make up the First and the Second Defensive
Doc 5: at war or preparing for war during the period 1563–1721. More than anything  of powerful fortifications built during the 1640s and 1650s, protected the.