The confluence of the Nemunas and Neris Rivers has been guarded by fortifications for ages. At first wooden castles guarded the settlements near the rivers. Later a stone castle was built in Kaunas at the confluence, which was destroyed by crusaders in 1362. Then New Kaunas Castle was built at the mouth of the Nevėžis, but before it was completed the crusaders, who built Gotteswerder Castle, constructed their own castle. And the Germans built Marienwerder Castle, either in the spot of the unfinished Old Kaunas Castle or next to it, which Jogaila destroyed in 1384.
At the beginning of the 15th century a serious artillery-resistant castle was constructed in Kaunas; following lengthy battles that ended in deadlock, battles at the Nemunas River subsided for a long. A city began to grow near the castle, which gradually expanded to include the Nemunas and Neris valleys. Only during the Livonian War when once again the internal regions of the Lithuanian State were in danger and the protectors of Kaunas began to worry was Kaunas Castle again reinforced, modernizing its defences. They began to consider city fortifications and the defensive wall of the city was built. The castle began to crumble, gradually washed away by the Neris.
In 1655 the Polish–Lithuanian Commonwealth experienced a deep crisis. The city of Kaunas was also greatly affected: it was occupied by the Russians, then the Swedes, and then the Russians again. Kaunas Castle, crumbling as it was, was used as a refuge for Russian garrisons anyway and was overcome only in 1661. Nevertheless, the defences of Kaunas Fortress would from then on be strengthened by foreigners: the construction of the city wall through Ąžuolų Hill (the Oaks Hill) was completed by the Swedes, the Russians established their base in the middle of the 18th century, and the French fortified the city at the beginning of the 19th century.
In 1879, once Russian-German relations deteriorated, the Russian Empire began to design a first class fortress in Kaunas. Work began in 1882 and in 1888 the Kaunas Fortress was considered to be in operation, even though there was a great deal left to the construction plan. The fortress was repeatedly modernized and in 1915, after heavy fighting, was occupied by the German army. For three years Kaunas was a German stronghold where the Eastern Front headquarters were located. The Lithuanian army was assembled and deployed in Kaunas in 1918-1920, fortress buildings had their own central offices, and in 1920-1940 attempts were made to customize the fortress to potential aggressors.
During World War II the stronghold of forts finally ceased to operate the functions of a combat fortress, but continued to be used for administrative and logistic German and Soviet military functions.
In 1993, after the withdrawal of the Soviet army and the Lithuanian army having taken over just some of the buildings, the fortress became civilian, seeking a new purpose and to serve the people. Tourists and others who used the fortress buildings became the main fortress soldiers, and substantial differences between the Medieval and new era of military heritage began to be less and less noticeable, becoming elements of the huge historical architectural Kaunas Fortress Park.