From Wikipedia,

Window tax was a property tax based on the number of windows in a house. It was a significant social, cultural, and architectural force in England, France, and Ireland during the 18th and 19th centuries. To avoid the tax some houses from the period can be seen to have bricked-up window-spaces (ready to be glazed or reglazed at a later date.)

Form a paper on The Biases of Thinking Fast and Thinking Slow,

The window tax must rank among the very worst taxes in the history of Western Civilization. The window tax in Great Britain (1696—1851) provides a remarkable case of tax-induced distortions in resource allocation. Tax liabilities on dwelling units depended on the number of windows in the unit. As a consequence, people boarded up windows and built houses with very few windows, to the detriment of both health and aesthetics. Using data from local tax records on individual houses, the analysis in the paper finds compelling evidence of such tax-avoidance and goes on to make a rough calculation of the excess burden associated with the tax.

A comment on economist Tyler Cowen’s blog, Marginal Revolution:

Bear in mind that a large window wasn’t limited to one pane of glass. Indeed, most windows were divided into small panes of the typical “bull’s-eye” glass that can still be seen today in many of them. Each pane was made by blowing a globe of glass which was then opened out and flattened (more or less) into a pane. The size of the pane was limited by the size of the globe that could be blown.

Larger windows were made by adding stone or wooden mullions to increase the structural strength. I suppose the limiting factor would have been the strength of the timber lintel supporting the wall above the window. For brick or stone structures, the arch could support almost unlimited spans (for the Church or the very wealthy.)