King William III of England needed money, so in 1696 he decided to implement a new property tax. To make sure the tax was progressive (i.e., affected the rich more than the poor), the parliament devised a seemingly clever idea: they’d use the number of windows as an index for the value of a house.
The assumption was that larger homes, presumably owned by the wealthy, would have more windows than the houses of the poor. All a tax assessor needed to do to calculate the tax was walk around a building and count the windows. Ingenious, no?
In its initial form, the tax consisted of a flat rate of 2 shillings upon each house and an additional charge of 4 shillings on houses with between 10 and 20 windows, or 8 shillings on houses with more than 20 windows.
You can probably imagine what happened next.