The substitute himself, a man of mystery, was kept in virtual imprisonment.  He was known as “Pavonius Nasor,” not because that was his real name, which was known to very few people, but because of an old legend that the ghost of a certain Pavonius Nasor, murdered centuries ago and never buried, still walked in the neighborhood of that part of the palace where the emperor’s substitute now led his mysterious, secret existence.

There were plenty of whispered stories current as to his true identity.  Some said he was an impoverished landholder whom Commodus had met by accident when traveling in Northern Italy.  But it was much more commonly believed he was the emperor’s twin brother, spirited away at birth by midwives, and the stories told to account for that were as remarkably unlikely as the tale itself; as for instance, that a soothsayer had prophesied how Commodus should one day mount the throne and that he and his twin brother would wreck Rome in civil war—­a warning hardly likely to have had much weight with the father, Marcus Aurelius, although the mother was more likely to have given credence to it.

Whatever the truth of his origin, Pavonius Nasor never ran the risk of telling it.  He kept his sinecure by mastering his tongue, preserving almost bovine speechlessness.  When he and Commodus met face to face he never seemed to see the joke of the resemblance, never laughed at Commodus’ obscenely vivid jibes at his expense, nor once complained of his anomalous position.  He appeared to be a man of no ambition other than to get through life as easily as might be—­of no personal dignity, no ruling habits, but possessed of imitative talent that enabled him, without the slightest trouble, to adopt the very gait and gesture of the emperor whom he impersonated.

As he strode ahead along the tunnel he received the guards’ salute with merely enough nod of recognition to deceive an onlooker not in the secret. (It was Pavonius Nasor’s half-indulgent, rather lazy smile that had persuaded Rome and even the praetorian guards that Commodus was an easy-going, sensual, good humored man.)

There was a box at one end of the private arena, over the gate where the horses entered, so placed as to avoid the sun’s direct rays.  It was reached by a short stairway from an anteroom that opened on the tunnel.  There was no other means of access to the box.  It’s wooden sidewalls, finished to resemble gilded eagle’s wings, projected over the arena so that it was well screened and in shadow.  There was none, observing from below, who could have sworn it had not been the emperor himself who sat in the box and watched Paulus the gladiator showing off his skill.

The assembled gladiators, perfectly aware of Paulus’ true identity, went through the farce of solemnly saluting as the emperor the man who stared down at them from beneath an awning’s shadow between golden eagle’s wings, and who returned the salute with a wave of the arm that all Rome could have recognized.