The Army Museum of Sweden (Armemuseum), founded in 1879 as an artillery museum (until 1932 it had been called the Artillerimuseum), is one of the largest depositories of flags of different eras and countries of the world, and houses approximately 4,500. The initial collection consisted of the military trophies of Swedish kings - Gustavus II Adolphus, Charles X Gustavus, Charles XI, Charles XII and their successors. The flags were kept in several Swedish castles and at the beginning of the 20th century were temporarily transferred to the Nordiska Museet.
laroslav Isaievych researched the features of the Cossack flags - trophies of the Lithuanian field hetman Janusz Radziwill, appropriated during the Kyiv campaign of 1651 - and provided visual images in his study. This research was conducted in the archives of Hetman Radziwill at the National Library of Russia in St. Petersburg, and was instrumental in identifying the original Cossack flags in the Swedish museum. The contemporary artist A. Westerfeld also depicted scenes of Hetman Radziwill's 1651 conquest and used some elements of the flags in his drawing. 

The two exhibited flags were captured by Hetman Radziwill during his conquest of Kyiv in 1651. 

Flag (1) of the Kyiv administrative military subdivisions. 
Mid-17th century. 
Silk; sewing, painting. 
112x227 cm. 
National Swedish Museums of Military History. Army Museum (Armemuseum), Swedish State Trophies Collection.

Flag (1) (yellow in color, with a cross, star, sun, and moon painted black; arm sleeve, painted black; edges made of Tercanela fabric) was captured in Kyiv and probably belonged to the Kyiv administrative military subdivisions. We have adequate documentation as to the ownership of the Kyiv flags - they were in the custody of the Kyiv magistrate. Radziwill most likely acquired them together with the keys of the city, which were handed over to him near the Golden Gates (on the square in front of St. Sophia?). This has been recorded by chronicles, who witnessed these events of the day. It became the subject of drawings by A. Westerfeld in which he recorded the triumphant entry into Kyiv of the Lithuanian hetman as he was met by the city's dwellers headed by the Metropolitan M. Kosov. Some are holding up the flags, others have lowered them. 
 

Flag (2) of the Chernihiv regiment. 
Mid-17th century. 
Cotton; sewing, applique. 
116x201 cm. 
National Swedish Museums of Military History. Army Museum (Armemuseum), Swedish State Trophies Collection. 

Flag (2) (overall red in color, with a white cross, a multi-colored center design, and a green star) belonged to the Chernihiv and Nizhyn regiments that fought in the Battle of Ripky on June 26, 1651 under the command of the Chernihiv regimnental colonel Martyn Nebaba.

Flags were the most desired and significant trophies of military conquests. Thus, during a ceremony at the Polish Sejm (parliament) in 1652, Janusz Radziwill, together with his cousin Bohusz Radziwill, presented the Polish king Jan II Casimir with 36 Cossack and Tatar flags as a token of loyalty and devotion. This event was reported in the foreign press, specifically in the «Gazette de France» in 1652. During the 17th and 18th centuries, military trophies, including flags, were traditionally reserved in royal palaces and churches. It is likely that during the Polish-Swedish war in the mid-17th century, these trophies found their way into King Gustavus' spoils.