Gion Matsuri(parade of Yamaboko) photo by photolibrary
Gion Matsuri is one of the three major festivals in Kyoto with Aoi Matsuri[葵祭（あおいまつり）](festival of Shimogamo and Kamigamo Shrine) and Jidai Matsuri[時代祭（じだいまつり）](festival of Heian Shrine).
Furthermore, that is also one of the three major festivals in Japan with Kanda Matsuri[神田祭（かんだまつり）](Tokyo) and Tenjin Matsuri[天神祭（てんじんまつり）](Osaka).
Gion Sairei-zu Byōbu
[祇園祭礼図屏風（ぎおんさいれいずびょうぶ）] (Right part):
This picture depicts the scene of Gion Matsuri.
Gion Matsuri was originally called "Gion Goryōe[祇園御霊会（ぎおんごりょうえ）]". Goryōe is a rite for appeasing ghosts which hold grudges. It was thought that they brought disasters and plagues.
In 869, a plague broke out throughout Japan. First Gion Goryōe was held in order to suppress the plague and people stood 66 spears(66 was the number of province at that time.) and 3 Mikoshi[神輿（みこし）](portable shrine) of Gion-sha[祇園社（ぎおんしゃ）](present Yasaka Shrine) were enshrined in Shinsenen Garden[神泉苑（しんせんえん）].
Gion Matsuri is held for a month and the highlight of festival is the parade of 33 Yamaboko[山鉾（やまぼこ）]s(float with decoration of spear) on July 17 and 24.
Yamabokos are carried around the area and performers play music called "Gion-bayashi[祇園囃子（ぎおんばやし）]". Especially, 90 degree turn of Yamaboko(That is called "Tsuji-mawashi[辻回し（つじまわし）]") is the great spectacle.
Each district around Yasaka Shrine owns its Yamaboko which has a different and various decoration.
Yoiyama[宵山（よいやま）] is also a popular festival. Yoiyama is held before the parade(July 14-16 and 21-23) and each Yamaboko is displayed at its own district.
photo by photolibrary
The events of Yamaboko was designated as an important intangible folk cultural property in 1979 and was registered as a UNESCO Intangible Cultural Heritage in 2009.