Black Low Heel Knee Boots Taking the popular riding-style boot silhouette and throwing in a few modern twists, Petra by Carvela is set to become an instant classic. Crafted from smooth cow leather for a high-quality look and feel, this knee-high boot in classic black is supremely comfortable with its flat sole, low 4cm leather stack heel, 28cm ankle circumference, 39cm boot shaft height, 25cm calf circumference and elastic panelling down the back of the leg for an easy fit. Gold buckle detailing on the back loop, an inside zip fastening and a smooth resin outside with a stitch-rand highlight smartly conclude the design.