Early morning of June 23, 1812. French Emperor Napoleon arrives to Aleksotas, the current district of Kaunas city.  Aleksotas was a part  of the Duchy of Warsaw  in 1812. 
Kaunas was a border town of the Russian Empire at the time. Two countries, namely the Russian Empire and the Duchy of Warsaw established by French Emperor Napoleon in 1807 of the Polish lands ceded by the Kingdom of Prussia under the terms of the Treaties of Tilsit, were divided by the River Nemunas. It covered the central and eastern parts of today’s Poland and minor parts of today’s  Lithuania and Belarus. Kaunas became a hot point of Napoleon’s invasion to the Russian Empire. 
The observation point of the Nemunas River crossing  was on the hill in Kaunas suburb Freda (currently Napoleon’s hill, height 63m, Piliakalnio str.) on June 24, 1812.   Napoleon observed on this hill French army entrance to Kaunas. 
​The French army crosses the Nemunas River using three pontoon bridges built during the night (220 000 soldiers in 4 days) and enters Kaunas. The troops had been joyfully met by the Government of Kaunas  that was occupied by the Russian Empire . But joy quickly turned into hatred. Unfortunately, the troops of the French army were mean to the locals:  they were robbing houses, stealing food, drinks, horses, plundering churches (especially  Pažaislis Baroque church ) and monasteries. They used churches as warehouses and accommodation for soldiers.
Napoleon  spent several days in Kaunas.  

He stayed  in the Carmelite ​Monastery  (Kaunakiemio str.40) and in the house located at Muitines str. 8 (now under possession  of Vilnius University) for 1 day.  The monastery also housed the headquarters of Napoleon (200 persons). The monastery was also an accommodation of the headquarters of Napoleon’s army (200 people).  The rest of the army stayed in the surroundings of Kaunas.
Napoleon and his  army returned to Kaunas from Russia on  the 7 of December, 1812. A defense of Kaunas had been organized by French Marshal Joachim Murat . However, the  local garrison consisted of only 1500 men (mainly Germans) 1500 men and had 42 cannons. Several of them were placed on the hills of Aleksotas for defense against the Russian army.
The last French soldier left Kaunas on  the 3 of December, 1812.
Approx. 40 000 troops were killed during  the battles against the  Russian army.  .
​A lot of  (5000-6000) French soldiers were killed and buried in Kaunas . The exact places of burial are not well enough known. The Cemetery of French soldiers in Silainiai , in the outskirts of Kaunas, near European route E67 (also known as Via Baltica) . 
Approx. 90 000 French troops in total were killed in Lithuania during the Napoleon's campaign against Russia.
A big festival Europeana. Napoleon in Kaunas 1812 dedicated to the 200th anniversary of Napoleon’s march across Europe and stay  was celebrated in 2012. 
The name Šančiai of one of the districts in Kaunas is derived from French word .  The reason for this is that a defense system was built here by Napoleon’s army when the troops had been crossing the Nemunas River in order to enter  Kaunas.  Lithuanians  had difficulty to pronounce chantier and it was changed to Šančiai.
A commemorative plaque was opened on the wall of the Carmelite Monastery to commemorate the fact of Napoleon’s stay in the house in 1812.
The biggest street in Šančiai district is named Prancūzų (French) because the French army marched through Kaunas to Vilnius down this road in 1812.

Napoleon hill

Please, open a link, for more information about Napoleon's invasion to Russia (Lithuania was also part of Russia (annexed at the end of 18 century)).