Ludus Magnus

Beside San Clemente, to the east of the Colosseum, you can see the ruins of ancient Rome's largest school for gladiators, the Ludus Magnus.
Inside there was a kind of miniature colosseum: two levels of travertine colonnades enclosed an oval arena with entrances on the long axis, still partly visible today

The authorities used to sit in stands along the short axis. Around the whole arena was the horse-shoe with its marble steps for the spectators. The small buildings you see on the Via Labicana side were the lodgings of the gladiators themselves.
They were really prisoners in these barracks and subject to the iron discipline of daily training sessions. There was even a special passage through which the gladiators were ushered directly into the Colosseum's underground chambers. In addition to the Ludus Magnus, which was the most important barracks, there were numerous other buildings attached to the Colosseum.
The Spoliarium was where the bodies of the athletes killed in combat were taken; the Sanitarium was where the wounded athletes were taken; and the Armamentarium was where the gladiator's arms were stored. Although these buildings were located close to the Colosseum, no ruins can be seen today.