The image above shows a Thracian on the left fighting a murmillo; the scene is a detail of a larger mosaic discovered at Bad Kreuznack, Germany, where it still can be seen.
For basic information on gladiators and how the day of a munus went, go here. The first gladiatorial bout was in 264 BCE, when Decimus Junius Brutus had 3 pairs of gladiators fight at munera (funeral games) for his father:
To honor his father, Decimus Junius Brutus was the first one to organize a gladiatorial munus.
Livy, Periochae Book 16
The late date may surprise, given how closely the gladiators are connected with Rome in our popular imagination – especially as chariot racing is known of in Rome from centuries before. Once the munera started, however, there was no looking back: In 216 Lucius, Marcus, and Quintus Lepidus had 22 pairs of gladiators at their father’s funeral games (Livy, From the Founding of the City 23.30.15); in 201 there were 25 pairs of gladiators sat the games for M. Valerius Laevinus; in 183 60 pairs of gladiators fought over 3 days in the munus for Publius Licinius – and so on, until Julius Caesar tried to have 300 pairs of gladiators fight at his father’s funeral games. (That was stopped by an anxious Senate, worried about the presence of so many gladiators in a violence prone Rome.)
No one knows for sure where the games came from: various origins have been proposed for the munera; sometimes they were said to be an importation from Etruria (where the Etruscans ruled); others said they came from the Samnites (an Italian tribe, once great enemies of the Romans). Modern scholars debate precisely where the games came from with very few agreeing on their initial source. However, it must be said that it was convenient for the Romans to represent shows of all sorts – including theatre – as coming from outside Rome, especially when passing moral judgment on the expense and lavishness of certain events. In the passage below Tertullian (c.160-c 240), a Christian author, fumes about the origins of the gladiatorial games in an extract from his work On Spectacles:
We still have to examine the most famed and popular spectacle: it is called munus from being an officium, for munus and officium are synonyms. People in the past thought they were performing a duty to the dead with this form of spectacle after they moderated its nature with a more refined form of cruelty. Long ago, since they believed that the souls of the dead are appeased by human blood, they purchased captives or slaves of poor quality and sacrificed them at funerals. Afterwards, they preferred to disguise this unholy practice by making it something to enjoy. Thus, after they trained the people they had obtained these ways to wield the weapons they had as best they could (training them to learn how to die!), they then exposed them to death at the tombs on the day appointed for sacrifices in honor of the dead. And so it was that they consoled themselves with murder. That is the origin of the gladiatorial munus. But gradually their refinement developed along with their cruelty; these inhuman people could not rest satisfied or gain pleasure unless wild animals tore humans to pieces. What was then a sacrifice offered for the appeasement of the dead was no doubt considered a rite in honor of the dead. This sort of thing is, therefore, idolatry, because idolatry, too, is a kind of rite in honor of the dead: both are services rendered to the dead.
Additionally, demons live in the images of the dead. And now consider the titles also: although this type of exhibition has moved from being an act to honor the dead to one which honours the living (for example, those who hold quaestorships, magistracies, flaminates, and priesthoods) still, since the guilt of idolatry taints the dignity of the title, whatever is carried out in the name of this dignity shares necessarily in the taint of its origin. We must also consider the paraphernalia which are considered as belonging to the ceremonies of the actual offices as also being idolatrous. For the purple robes, the fasces, the fillets, and crowns–finally, also, the announcements made in meetings and on advertisements and the final dinners given the evening before games—have the Devil’s pageantry and the invocation of demons. In conclusion, what shall I say about that horrible place which not even perjurers can bear? For the amphitheatre is consecrated to more numerous and more terrible names than the Capitol, although the Capitol is the temple of all demons. There as many unclean spirits live as there are seats. And to say a final word about the arts concerned, we know that Mars and Diana are the patrons of both types of ludi.
Tertullian, On Spectacles 12
Proponents of an Etruscan origin often point to a painting of a possible venatio/damnatio ad bestias on the Tomb of the Augurs in the Etruscan city of Tarquinia, which also shows wrestling and other funeral games. In this image a man is clearly being attacked by a dog which is being set on him by someone else; the painting dates from c. 530 BCE. However, proponents of a Campanian origin can point to Lucanian frescoes from Paestum, a Campanian city, which show boxers, chariot racing, and two warriors fighting each other. These were all clearly events at funeral games, but we have no way of saying if the warriors fighting were gladiators or members of the community competing at the games for prizes. Campania is also where the first stone amphitheatres were built – Pompeii had one in 70 BCE – and also where many of the gladiatorial ludi were. Capua, another Campanian city, was where the revolt of Spartacus broke out also; it also had a stone amphitheatre before Rome did.
 No, they’re not. Both mean duty, but munus also means gift, especially a gift given to the dead.
 A type of priesthood.
 Certain Roman magistrates (consuls, praetors, curule aediles, quaestors) were entitled to be accompanied by lictors who carried fasces, a bundle of rods with an axe sticking out. These symbolized their power to punish as part of their duties.
 The bands of wool priests and priestesses wore on their heads when performing ceremonies.
 We actually still have some advertisements for these shows from Pompeii.
 The cena libera, a public feast given the night before ludi to gladiators and those who were due to be executed in the arena.