On some yagura and most main keep there are places just above the stone walls that slightly protrude from the main structure. These are not decorations but innovative tactical devices called ishi-otoshi (rock chutes). From these chutes defenders within the main keep (or yagura) could pour rocks or even boiling oil or water down on anyone attempting to scale the walls. The above picture shows 2 such devices on a section of yagura at Matsuyama-jo.