From 1696 to 1851, England taxed houses based on the number of windows they contained. The window tax was introduced under William III as a workaround for an unpopular hearth tax that the government had repealed a few years earlier. Income was hard to measure. Property was easier. The number of windows on a house, the reasoning went, was a rough proxy for the size of the household behind them, and therefore for wealth.

The structure changed over the years, but always followed the same shape: a flat charge for any inhabited house, plus an extra rate per window above a threshold. In some periods the threshold was as low as seven windows. The wealthy were meant to pay more. In practice, what they did instead was reduce the count.

Owners across England bricked up their existing windows. Some did it before the next assessment to fall under the threshold. Others did it to lower the per-window rate. Stone or brick was inserted into the openings, often without removing the surrounding frame. Whole rows of upper-floor windows were sealed shut. Tenants in rented buildings lost light and air. Hospitals, factories, schools, and especially crowded urban tenements — buildings whose function or layout naturally required many windows — were hit hardest.

By the early 19th century, doctors were arguing publicly that the tax was actively damaging public health. Less light meant less ventilation, which meant more tuberculosis, typhus, and other respiratory diseases in dense housing. Reformers, including Charles Dickens, attacked it as a tax on light and air. Petitions piled up.

It was repealed in 1851 and replaced with a tax on house value.

Walk through any older English town today and look at brick buildings from the 18th and early 19th centuries. The bricked-up rectangles are still there, set into the walls — a stone-and-mortar record of a tax that is older than most of modern Britain.