Emperor Seiwa
The actual site of Seiwa's grave is known.  This emperor is traditionally venerated at a memorial Shinto shrine (misasagi) at Kyoto. The Imperial Household Agency designates this location as Seiwa's mausoleum.  It is formally named Minooyama no misasagi.  From the site of his tomb, he was sometimes referred to as Mizunoo (水尾).