The way that the windows jutted out beyond the building also allowed for extra space. She said this particularly helped in foggy San Francisco. “At the time they were built, were relying on gas lighting, and the interiors were painted dark to cover up soot from the gas lights and soot from coal burning.” “You get more light when you incorporate a bay window, and Victorians took advantage of that,” Bonnie Spindler, a real estate agent and “the Victorian Specialist” of San Francisco, said. They continued in popularity through the Victorian era, when so much of the architecture was lauded for its function. The bay window most San Franciscans think of - the one exhibited on a classic Victorian like the Painted Ladies, for example - is a specific type of two shorter windows and one longer window that come together at angles to form a “bay.” Tim Kelley, a consultant and historic preservation advocate in San Francisco, said they began appearing in the city in the late 1880s. This explains why the windows are still found so frequently in cities across the globe, with notable prevalence in the U.K. It’s unclear when exactly bay windows were “invented,” but they rose in popularity during the English Renaissance, booming during the early 16th century to the early 17th century. The style of windows actually predates the Bay Area. The quintessential bay window isn’t just found on Victorians - more on that later - but it’s become as synonymous with the Bay Area as fog or the Golden Gate bridge. A curving bay window wrapped into the facade is a signature piece of Bay Area architecture - even if it really doesn’t have anything to do with the Bay Area at all. But there’s a key feature of this image that’s easy to overlook, though it would make the scene very odd without it. When you picture a residential street in San Francisco, it’s likely that your brain conjures up a row of ornate, colorfully painted Victorian homes all tucked together on a steep hill. DEA / GIANNI OLIVA/De Agostini via Getty Images