In the Heian period, on the outskirts of Tomo were built Seikan-ji Temple by Saicho (founder of the Tendai sect of Buddhism in Japan) and Io-ji Temple by Kukai (founder of the Shingon sect of Buddhism in Japan), serving as the hubs of the both Tendai and Shingon teachings, respectively, to be spread over the southern Bingo Province.
平安時代には鞆近郊に最澄により静観寺、空海により医王寺が創建され、備後国南部における布教の拠点となった。