The cats have been in the museum, that was once a palace, since the 18th century. In 1774, Empress Elizabeth of Russia gave an order for cats to come live in the palace to control the mice population. James Rodgers of the BBC said it is thought that the cats first came from Kazan, a city known for having cats good at catching mice. The cats stayed in St. Petersburg except during World War II, when the existing cat population was killed. After the war, a new group of cats was brought in because the rat population had increased.