Aoi Matsuri began as a way to please the Kamo gods (who are associated with thunder and weather) after a series of severe storms caused famine and disease.
The festival takes place at Shimogamo Shrine. It begins with a demonstration of yabusame (mounted Japanese archery) on May 3rd.
On May 12th there's a religious procession of around 100 people dressed in Heian period costumes. The procession stops in front of Kyoto's ancient sacred forest (Tadasu no Mori) for dancing and singing. The ceremony welcomes a god (Aramitama) to the festival.
The main event takes place on May 15th. A Heian period imperial procession is reenacted. Around 500 people dressed in the imperial style of the Heian Period (794-1185) walk from the Imperial Palace to the Shimogamo Shrine.
The Aoi Matsuri is ranked #10 of 100 best festivals in Japan