A summer festival traditionally held at shrines dedicated to Gozu tenno or Gion. These used to be widespread in Japan but appear either to have declined or been renamed gion matsuri since the Meiji period. There is a surviving tenno matsuri (also known as Tsushima matsuri) held at the Tsushima jinja in Aichi on the fourth weekend in July. It features a flotilla of towering, wide 'danjiri' boats (see Tenjin matsuri) which float down the Tenno-gawa river on the evening before the main festival day.
A Popular Dictionary of Shinto. Brian Bocking.