The shrine's Heian period connections with the Kyoto and the Imperial family date from its founding in 859 when construction on its earliest structures commenced. Shrine tradition explains that Emperor Seiwa ordered the shrine to be built in obeisance to an oracle in which the godHachiman expressed the desire to be near to Kyoto to watch over the city and the Imperial House of Japan. This vision was reported by a Buddhist monk, Gyōkyō, who had a second vision which led to selecting the Otokoyama location where the shrine now stands. Like other Hachiman shrines, until 1868 Iwashimizu was actually a shrine-temple complex called Iwashimizu Hachimangū-ji dedicated to Buddhism as much as to kami worship. The shrine became the object of Imperial patronage during the early Heian period. In 965, Emperor Murakami ordered that Imperial messengers were sent to report important events to the guardiankami of Japan. These heihaku were initially presented to 16 shrines including the Ōharano Shrine. The shrine's importance and influence grew in succeeding centuries; and its extensive landholdings led to modest conflicts with Minamoto no Yoritomo during the years in which the Kamakura shogunate was establishing itself. The shrine sought to maintain its traditional exemption from contributing to paying the costs of military forces. In time, the bakufu faded away; and the shrine endured. Iwashimizu Hachimangū and Ise Shrine were specified for "the two ancestral mausoleum" in the Middle Ages.
1456 : Ashikaga Yoshimasa visited Iwashimizu Shrine; and all the officials of the Daijō-kan joined him in going there.
From 1871 through 1946, Iwashimizu Hachimangū was officially designated one of the ''Modern system of ranked Shinto Shrines, meaning that it stood in the first rank of government supported shrines. Other similarly honored Hachiman shrines were Usa Shrine of Usa in Ōita Prefecture and Hakozaki-gū of Fukuoka in Fukuoka Prefecture.
Imperial progresses to the shrine
In 979, Emperor Enyū visited the shrine; and the shrine continued to be visited by nearly all the emperors until the reign of Emperor Go-Daigo, when the sovereigns began to live more secluded lives. In the Shōhei era, Emperor Murakami visited Iwashimizu in person. After the Ōnin war, Imperial visits were held in abeyance for 200 years.
The shrine is dedicated to the veneration of Hachiman, the Shinto kami or spirit guardian of Imperial legitimacy. Since the time of its founding in 859, Hachiman has been recognized as Emperor Ojin.
Treasures
A 2005 survey of the treasures at Iwashimizu revealed, among other things, the existence of a kris, a jeweled Indonesian dagger, which was exhibited at Kyoto National Museum as part of an exhibit entitled "Famous Swords from Kyoto's Temples and Shrines."
