Mushiko-mado (虫籠窓)

A mushiko-mado is a plastered window on the first floor of a machiya and is most commonly found on houses of the tsushinikai type. Because the bars of plaster resemble a Japanese insect cage, their name literally translates to "insect cage window". 

They were added to the houses during the Edo period (1603–1867). Fires were frequent and numerous during that time and the plastered bars were put in place as a measure to prevent fire from spreading. Another tale, which is not verified, says that the bars were put in place so that commoners could not look down upon samurai passing on the street, which was a punishable offense in feudal Japan.