|Bronze-Iron Age buttons as ornament. [source]|
the earliest known being found at Mohenjo-daro in the Indus Valley [now Pakistan]. It is made of a curved shell and about 5000 years old. [Ian McNeil, An Encyclopedia of the History of Technology]Rows of buttons as a necessary part of clothing were unknown. Usually a single button—a flat decorated surface with a loop attached to the back—was put on clothing to pin up a single fold of fabric.
The first evidence of "functional buttons"—used to attach clothing so that it fit snugly about the body—is found in art. Statuary on the Adamspforte ("Adam's gate") at Bamberg Cathedral (carved c.1235) in Germany shows a button holding clothing together.
By the late 1300s, buttons were being applied to all sorts of clothing in order to make it fit more closely to the body. One of the modifications that made buttons work well was the addition of reinforced button holes to clothing, which spread in the later 1200s.
|A late medieval button from England [source]|
This seems odd to the modern age, because we take form-fitting clothing for granted. Didn't they have looms and weaving? Of course. But much form-fitting fabric in the Middle Ages didn't appear until the development of knitting.
But that's a story for another day.