This rounded object, presumably either a column drum or base, was partially roughed-out while still attached to the rock-face. This is a common technique for rounded elements, especially column shafts, which enabled the quarrymen to identifying any faults in the stone before the whole object was quarried. In this case a crack in the stone did reveal itself and led to the halting of work.
This object is from one of the more than seventy individual extraction points which constitute the so-called City Quarries at Aphrodisias, located roughly 2 km north of the city. White and grey marbles were quarried in this area.