As nomads became settlers and built structures to live in for extended periods of time, they were basic—a floor, a roof, and four walls—and local woods or stones were the only construction materials available.
Over time, these simple structures got more complicated as separate rooms were devised for various uses—a common room for living, a kitchen with a chimney for cooking, and smaller rooms fit a bed for sleeping. Much later and smaller still, water closets for toilets and baths.
Less migratory, longer term storage solutions were needed for possessions acquired. Yet instead of closets—the tiniest of rooms within rooms—small multi-purpose furniture pieces were popular, and still movable.
From the Latin ‘armare’ to arm, and ‘armarium’ a chest or safe for arms—originally armoires were box-like chests with flip-top lids. At some point, they were turned on their sides and lids became doors which were quite large as they completely covered the box of the cabinet.
In the Middle Ages, French and English Royalty intermarried so naturally they shared their lifestyles—which might explain why ‘armoire’ and ‘wardrobe’ are interchangeable. Originally ‘guards of the robes’, wardrobes preserved and protected household textiles and clothes as more of each were required for various duties and events—and once more wealth was had to purchase them.
As migration from the countryside to large cities occurred during the Industrial Revolution, ingenious methods of construction were developed so that wardrobes could be taken apart and re-assembled in small Victorian bedrooms once gotten through narrow doorways—perhaps the earliest of ready-to-assemble (RTA) or knock-down (KD) furniture.
Ironically, just as plain box-like chests were multi-purpose hundreds of years ago, the same applies to the a symmetric closet which can be used for home office supplies, craft storage—or a hall closet.