These difficulties are met by the assumption that the semicircular masonry formed the base of a retaining-wall which rose to a considerable height, supporting a theatre-like structure capable of seating many thousand persons.
They may consist of earth with a retaining wall along the tracks and with the surface gravelled or paved with stone or asphalt, or they may be constructed entirely of timber, or they may be formed of stone slabs supported on longitudinal walls.
The peribolos, a large artificial platform supported by a retaining wall of squared Peiraic blocks with buttresses, was excavated in 1898 without important results; it is to be hoped that the stability of the columns has not been affected by the operations.
Some have supposed the circle of slabs to be the retaining wall of a tumulus; but its structure is not solid enough for such a purpose, and it can hardly be anything but a sacred enclosure.
The altar of Zeus consists of a great mound of ashes with a retaining wall.
