Many of the graffiti made by gladiators, including those of Celadus and Cresces, were found scratched on the columns of the peristyle enclosing a central courtyard, which was surrounded by a portico and a series of small rooms used to house the familiae gladiatoriae. These barracks were damaged by the earthquake of AD 62 and the gladiators transferred to the quadriporticus of the theater, which was converted into a training school (ludus). It was here that were found much of the armor discovered at Pompeii, including helmets, greaves, belts, and the shoulder piece worn by the retiarius, some of which were stamped NER or NER.AUG, indicating that the belonged to the Neroniani, gladiators from the imperial school at nearby Capua, to which Nero had given his name.
Here, too, was found the skeletons of a lady adorned with jewels and that of her gladiator lover. As poignantly, there also was a graffito scratched on the wall of the dining hall (which could hold no more than two hundred men): "The philosopher Annaeus Senecas [sic] is the only Roman writer to condemn the bloody games."
On the right of the amphitheater itself, one can see the quadriporticus located behind the large theater at Pompeii, a pool apparently situated in the center of the courtyard. The fresco now is in the Museo Nazionale Archeologico (Naples).
References: Gladiators at Pompeii (2003) by Luciana Jacobelli; The Story of the Roman Amphitheatre (2000) by D. L. Bomgardner.