Whilst, taking in the beauty of the scene, Dante becomes aware of the nearby presence of an old man, Cato of Utica. Cato is puzzled by the appearance of Dante and Virgil:-
I saw beside me an old man alone,
worthy of so much reverence in his lock,
that more owes not to father any son.
"Who are you? Ye who, counter the blind river,
have fled away from the eternal prison?"
moving those venerable plumes, he said.....
Cato, who lived in the first century BC, was regarded in medieval times as the supreme example of moral worthiness. That he, a non Christian who committed suicide rather than surrendering to Caesar, is the guardian of the way to Purgatory is puzzling.
But the ascent of the mountain is a moral progress in which the natural virtues are purified and strengthened by Grace. Cato remains on the shores of Purgatory. He is a moral imperative founded in duty rather than in love, since Purgatory is for those whose lives are founded upon love rather than duty. Virgil explains his mission and Cato allows them to pass. He instructs Virgil to bind a reed around Dante's waist and to wash his face in order to remove all the stains of Hell . As Virgil plucks a reed from the ground another springs up in its place - the first miracle of Purgatory.