Did Medieval Castles Have Glass Windows?

Middle ages castles typically featured minimal or no glass windows for a long time. Instead, they often included small openings, also known as arrow slits, to provide lighting and ventilation while maintaining defensive purposes. These designs were particularly prevalent in the earlier stages of medieval architecture (around the 12th and early 13th centuries).

The Late Medieval Period and the Rise of Glass Windows

By the late medieval period, particularly during the 14th and 15th centuries, glass windows began to appear, albeit on a limited scale. This development was more prominent in affluent castles and manor houses. The windows were often small and manufactured from leaded glass, which consisted of tiny glass panes held together by lead strips. Despite this evolutionary step, the widespread use of glass windows was still uncommon compared to later periods. Many castles continued to rely on wooden shutters or other materials to cover openings.

Pre-16th Century Windows in England

Pre-16th century England saw a diversity of window styles and materials. Most windows were constructed from stone or timber with unglazed openings, which could be covered using various methods such as oiled cloth, paper shutters, or thin sheets of horn. Glazed windows were reserved for the highest-status buildings and were typically small panes of glass set in lead strip latticework. This luxury was reserved for those with significant wealth.

Development of Glass Making and the Rise of Glazed Windows

During the Roman era, glass-making was an advanced process, and many ancient homes featured glass-paned windows. Early windows consisted of glassy pebbles set within wooden frames, allowing some light to pass through but not completely transparency. Clear glass panes were first created in the late 3rd century CE when glassmakers began blowing cylindrical bubbles and slicing and flattening them. This breakthrough in clear glass development, which was so crucial for windows, was eventually lost during the period known as the Dark Ages.

During this period, domestic windows remained unglazed, with wooden shutters providing insulation against the cold. Some inventive homeowners used oil-soaked animal hides or parchment, making them as translucent as possible. The size of the windows was also minimized to reduce drafts, and additional insulation came from curtains or mats. As a result, interiors were typically dark compared to modern standards, with fires providing most of the light.

Revival of Glass Technologies in the Middle Ages

During the Middle Ages, glassmakers began to rediscover and refine techniques for making flat window glass. In the 14th century, French glassblowers developed the crown glass process, one of the most influential innovations in window-making history. This method involved spinning a hollow glass bubble into a flattened disc using centrifugal force. As a result, the windows looked like bottle bases inside lead panes. Meanwhile, other glassmakers revived the ancient cylinder glass technique, creating small squares of glass.

The introduction of these advanced technologies made it possible for the wealthy to install more windows in their homes. Houses of the very rich increasingly featured glass windows in the central, important rooms. By the mid-16th century, window glass had become more widespread, although it was still considered a luxury. Upper-class houses might only have glass in the most important rooms, while better-off middle-class homes had glass in approximately half their windows. For the aristocrats, window glass was so precious that they had it stored carefully during their absences from their various estates.