Children play outside III fort in December, 2016. Some...

KAUNAS FORTRESS, KAUNAS, LITHUANIA - 2017/01/15: Children play outside III fort in December, 2016. Some sections of the fort were used as housing for the poor during the interwar years. They suffered from inadequate ventilation, water damage and virtually non-existent daylight. Historic photographs can be seen in the Fortress Museum, found in the IX fort. Russian Tsar Alexander II, chose Kaunas, Lithuania as the location for the most modern fortress in the Russian Empire. Found in a strategic location in the middle of two rivers, the city has long stood as the barrier between East and West during the Teutonic conquests, Nordic Wars, Napoleonic Wars and both World Wars. Following the construction of thirteen forts - complete with weapons infrastructure, military hospitals and churches - every third man in Kaunas was a soldier in the Russian Tsars army. In the onset of World War One, the fortress fell in just over a week, taking the lives of 20,000 defending soldiers with it. (Photo by Benas Gerdziunas/SOPA Images/LightRocket via Getty Images)