fenestration

Latin fenestra — window — may derive from a Semitic root (compare Hebrew 'ayin, 'ayin, or Phoenician forms meaning 'opening, eye'). The Indo-European root theory derives it from PIE *bʰeh₂- (to shine), but the Semitic borrowing theory has also been proposed. Whatever its ultimate origin, fenestra named the opening in a wall that admitted light and air — before glass, this was simply a hole.

Roman windows were typically unglazed or covered with thin sheets of mica or selenite (translucent minerals) — glass windows were available but expensive. The Romans used wooden shutters for protection. The word fenestration in architectural use means the pattern, proportion, and placement of windows in a facade — one of the primary determinants of a building's character.

The development of plate glass in the 17th century — followed by the plate glass revolution of the 19th century — transformed fenestration. Suddenly, windows could be large; the facade could be more glass than wall. The Crystal Palace (1851), designed by Joseph Paxton for the Great Exhibition in London, was an iron frame supporting 293,655 panes of glass — the first entirely fenestrated building, a building that was its windows.

Le Corbusier's Modulor system (1948) included specific proportions for windows — his 'horizontal window' was a polemical statement against the vertical window of classical architecture. The orientation of the window — vertical or horizontal — is as much an ideological statement as a functional one. Modern architecture's floor-to-ceiling glazing is a century-long argument about what fenestration should mean.