Nike Adjusting Her Sandal, Temple of Athena Nike, Acropolis.
Sculptures in stone used a variety of chisels – pointed, flat, and clawed – to chip away at the stone, using hammered blows at various angles to create their effects. The running drill, in use about the 5th century, permitted sculptors to shape finely crafted grooves and channels, thus allowing for some of the more exuberant and expressive drapery effects popular at this time.
The influence of the drapery effects from the Parthenon pediments – those wet or wind-blown looks - may be felt in Greek sculpture – almost literally – throughout the last quarter of the 5th century BCE. The Acropolis was home to several temples, one of which, the Ionic Temple of Athena Nike, was adorned with especially striking reliefs on the parapet showing various Nikes (Nicai, pl for Nike). Sculpture in high relief like this lends itself to especially expressive contrast effects, from deeply cut grooves and the higher swirls they create, and from the contrast of flat with rippled surfaces generally. Modeling lines allow sculptures to create linear patterns in drapery that reveal the lines and shapes of the body beneath.
A catenary is the curve a suspended line makes when hung from equal points; in Greek sculpture it refers to the drapery effect created when a series of such lines are formed by fabric, often falling from the shoulders around the neck and around the breasts. The catenary pattern of parallel lines is an especially pleasing method of giving the drapery the springy qualities of actual fabric and of modeling the human anatomy it both covers and reveals.
This celebrated pose doesn't seem to tell a story or evoke a character or event; its a woman - albeit a Nike, the goddess of victory, reaching down to fix the strap of a sandal, whether tightening or loosening its hard to say. It is as if the sculptor wanted to show off some particularly interesting things he had discovered about the relationship between drapery and the female anatomy, or as if he wanted to create a piece out of a largely elliptical or hyperbolic shapes.
Whatever... The absent head is not missing.