cortina

Curtain, in its architectural sense, comes from the Latin cortīna (curtain, hanging, enclosure), possibly from cohors (courtyard, enclosure). In castle terminology, a curtain wall is the section of defensive wall that connects two towers or bastions. The towers are the anchor points. The curtain hangs between them. The metaphor is textile — a stone wall described as if it were cloth.

Curtain walls were the most vulnerable part of a castle's defenses. Towers could withstand battering rams and undermining better than the flat stretches between them. Besiegers targeted curtain walls for breaching. Military engineers responded by thickening curtain walls, angling their bases (to deflect missiles and prevent mining), and adding flanking towers close enough together that defenders in adjacent towers could fire along the base of the curtain wall.

Edward I's castles in Wales — Caernarfon, Conwy, Harlech, Beaumaris — represent the peak of curtain-wall design. Beaumaris, begun in 1295 and never finished, has two concentric rings of curtain walls with towers at regular intervals. The inner walls are higher than the outer, allowing defenders on both rings to fire simultaneously. The design is textbook concentric defense, and the curtain walls are its primary element.

In modern architecture, 'curtain wall' means something completely different: a non-structural exterior wall, typically glass, that hangs from the building's frame like a curtain. The Lever House in New York (1952) was one of the first curtain-wall skyscrapers. The word made the same journey twice — from textile to stone, then from stone to glass — each time describing something that hangs.