Tensuioke (rain barrels), old Japanese fire prevention technique

An ingenious fire prevention method devised by the medieval Japanese constructors was to collect rain water directly on the roof, in wooden barrels called tensuioke - which actually means "rain barrel".

You can see this technique built on the roof of the Kongobuji at Koya-san. In case of a fire alarm, the barrels on top of the roof were quickly emptied over the layers of hinoki Japanese cypress bark shingles.