The Aoi Matsuri is one of Kyoto's three most famous festivals (along with the Gion Matsuri and Jidai Matsuri) and takes place every May 15. The festival's main attraction is a large parade in Kyoto, in which over 500 people dressed in the aristocratic style of the Heian Period (794-1185) walk from the Imperial Palace to the Kamo Shrines. Aoi is Japanese for Hollyhock, and the festival is named after the Hollyhock leaves that are worn by the members of the procession.

Predating Kyoto's establishment as the national capital in 794, the Aoi Matsuri began in the 7th century, although its precise origins are uncertain. There were most likely natural disasters occurring that were believed to be caused by the deities of the Kamo Shrines. After the Emperor made offerings to the gods, the disasters subsided and a tradition was begun. The festival's official name remains Kamo Matsuri, because of its association with the shrines.

(Quoted from Kyoto Travel: Aoi Matsuri (Aoi Festival) (japan-guide.com)