As everyone knows, gladiators entering the arena in ancient Rome faced the emperor and shouted, "We who are about to die salute you." Defeated combatants would have their fate decided by a thumbs up or a thumbs down from the crowd, or by the emperor himself.

Not really, says the Dutch historian Fik Meijer in "The Gladiators." It was not gladiators who uttered the immortal salute, but 9,000 prisoners about to engage in a mock sea battle on Lake Fucino organized by the Emperor Claudius, and described by Suetonius. The sentiment made no sense for gladiators, who expected to vanquish their opponents and live. The pollice verso, or "turned thumbs" signal, remains ambiguous. Historians do not know exactly what the gesture looked like.

Mr. Meijer, a professor of ancient history at the University of Amsterdam and the author of "Emperors Don't Die in Bed," understands exactly what readers want to know about gladiators and anticipates their every question in this admirable little study. He explains who the gladiators were; how they were trained, fed and paid; what weapons they used; and what rules governed combat in the arena. One chapter reconstructs a full day's program at the Roman Colosseum and, as a bonus, Mr. Meijer looks at two films, "Spartacus" and the more recent "Gladiator," to see just how well Hollywood captured the flavor and the period detail of Rome's most popular sport.

The elaborate, theatrically produced entertainments associated with the Colosseum and hundreds of smaller amphitheaters throughout the empire had their heyday in the first and second centuries A.D., but for many centuries before that, gladiators had engaged in hand-to-hand combat during funeral rites for important Romans. In so doing, Mr. Meijer writes, they illustrated "the virtues that had made Rome great, virtues demonstrated by the deceased himself during his lifetime: strength, courage and determination."

Over time, the increasingly elaborate private rites evolved into lavish public spectacles intended to boost the prestige of the emperors. The sport became professionalized, with managers, a fixed schedule and training centers, where gladiators developed expertise in one of the dozen or so weapon specialties on offer. Under Augustus, the games achieved a variety and splendor never before seen. In his political will and testament, he boasted that in the eight gladiatorial contests he had held, 10,000 men had fought to the death.

The gladiator was a contradictory figure. Socially, he was a despised outcast, the lowest of the low, but the warrior code and the unflinching courage displayed by most gladiators made them, in a sense, ideal Romans. Recruits were generally prisoners of war, like Spartacus, or slaves charged with crimes, but former soldiers, lured by the prospect of prize money, or well-born Romans entranced by the allure of the arena, often signed contracts to fight as gladiators. Even emperors occasionally took up sword and shield, descending into the arena for a bit of carefully staged combat. Commodus (played by Joaquin Phoenix in "Gladiator") regularly appeared as a gladiator under the stage name Hercules the Hunter.

Not surprisingly, gladiators captured the public imagination. They were celebrities. Young women left amorous graffiti on the walls of the gladiator schools, or wore hairpins shaped like swords or spears. Even the wives of the emperors, it was rumored, occasionally enjoyed secret liaisons with gladiators. Some women became gladiators themselves, fighting regularly in shows staged by Nero. The emperor Septimius Severus, unamused, banned female combat in A.D. 200 as an affront to military dignity.

Fame came at a heavy price. Mr. Meijer estimated that most gladiators, fighting two or three times a year, probably died between the ages of 20 and 30 with somewhere from 5 to 34 fights to their names. One gladiator, Asteropaeus, notched 107 victories, and exceptional gladiators fought on into their 40's and 50's, sometimes retiring as free men. But these were the exceptions.

The "sport" was appallingly brutal, and many gladiators faced the arena with fear and trembling, especially those who were assigned to square off against wild animals. On one occasion, 20 gladiators committed group suicide, killing one another one by one, rather than enter the arena.

Even successful gladiators lived an exceptionally hard life. Like modern boxers, they were exploited by their managers. Victory usually brought an olive branch or wreath, plus a few small coins. Only a few shows offered the kind of prize money that could guarantee a comfortable life. Lucky gladiators found work as bodyguards for noblemen, but more often, those past fighting age took menial work at the gladiator schools and eventually ended up destitute, begging for alms.

Historians have very little specific information about gladiator fights. There were rules, and a referee, but the rules remain unknown. Some of the gladiatorial specialties remain obscure. The dimachaerus, or "man with two swords," is mentioned in two inscriptions, but there are no pictorial images of him, so it is impossible to know how he fought. Nevertheless, Mr. Meijer, relying on snatches of verse, historical passages, mosaics, sculpture and funeral inscriptions, manages to summon up the savage thrills of the Colosseum.

A few things we do know. Kirk Douglas should not have faced off against a gladiator with trident and net in "Spartacus," since that form of combat would not appear for another 60 years. Russell Crowe, in Roman times, would not have fought a gladiator and a tiger simultaneously as he does in "Gladiator." Even in Rome at its most barbaric, there was a right way and a wrong way to throw a man to the beasts.