We entered a narrow opening, some twelve feet high, which ran perhaps twenty yards into the cliff.
Lenormant supposes that this was a quarry made by the original Greek colonists.

If Cassiodorus used it for the purpose mentioned, the cave must have been in direct communication either with the sea or the river; at present, many yards of sloping shingle divide it from the line of surf, and the river flows far away.

Movement of the shore there has of course been, and the Pellena may have considerably changed the direction of its outflow; our author's description being but vague, one can only muse on probabilities and likelihoods.
Whilst we talked, the entrance to the cave was shadowed, and there entered one of the men who had turned back half-way; his face betrayed the curiosity which had after all prevailed to bring him hither.
Shouting merrily, my companion hailed him as "Brigadiere." The two friends contrasted very amusingly; for the brigadiere was a mild, timid, simple creature, who spoke with diffidence; he kept his foolishly good-natured eyes fixed upon me, a gaze of wonder.

After listening to all that my guide had to say--it was nothing to the point, dealing chiefly with questions of railway engineering--I had just begun to explain my interest in the locality, and I mentioned the name of Cassiodorus.

As it passed my lips the jovial fellow burst into a roar of laughter.