Eszék (Osijek, Essegg) used to be guarding the Kingdom of Hungary from the south.
Let us not forget that the Kingdom of Croatia and the Kingdom of Hungary had been in Personal Union for 816 years. Now, it is in Croatia.
The earliest recorded mention of Eszék dates back between 1030-1043 in the Via Hireosolymitana which noted the town as a good crossing place of the Dráva river where the Crusaders toward the Holy Land could get lots of bread.
The town was a feudal property of the Hungarian Kórógyi family between 1353 and 1472. After the death of the last Kórógyi, King Matthias Corvinus granted it to the Rozgonyi family.
The city and the previous bridge of Eszék were destroyed by the Ottoman conquerors on 8 August 1526. The Ottomans defeated the Habsburgs’ army here at 1537.
The Turks rebuilt the town in Ottoman oriental style and it was mentioned in the Ottoman census of 1579. In 1566, Sultan Suleiman built a famous, 8 kilometer-long wooden bridge of boats in Eszék, considered at that time to be one of the wonders of the world. It was one of the most important crossing places and had a major role in the logistics of the Ottoman army.
In the Ottoman Empire, Eszék was part of the Budin Eyalet. General Pálffy Miklós managed to burn the bridge in 1599 and Zrínyi Miklós (also known as Nikola VII. Zrinski, the great-grandson of Nikola Subic Zrinski, the hero of Szigetvár) did the same in 1664 during his famous Winter Campaign.
Eszék was liberated by the Habsburgs on 29 September 1687. As the Hungarian inhabitants and all Croatian and others had vanished from the city, German settlers were brought there in 1687.
Here are pictures of Eszék / Osiek (mainly from http://www.varak.hu) :