The Toga: badge of Roman citizenship.

photo Toga Party Costumes - Buzzle

Toga was THE national garment of Roman citizens:  a woollen cloak with curved hem.
For men it was a symbol of their free-born status. 
Augustus revived the toga and invited Romans to wear it in the Forum and when attending races at the Circus.

Late antique writer Macrobius describes in his 'Satires' (3.13.4) the complexity of being a dandy for Hortensius: [...] to go out well dressed he checked his appearance in the mirror, and so draped the toga on his body that a graceful knot gathered the folds, arranging them not randomly but with care [...] He thought it a crime that folds should be moved from their place on his shoulder [...]

It was a statement which underlined the Roman citizenship.
Initially it was made of undyed white thick coarse woollen cloth.
A dark toga: brown or black (toga sordida) was used by poor citizens, accused people or for mourning.
Victorius generals in their processions wore the special toga picta (purple wool and gold thread).  Also worn by kings initially, emperors later, equites and priests.
The toga praetexta was for high rank people:  it had a purple stripe (clavus).
Young Roman boys, once they turned 16,  were allowed to wear the toga virilis or liberior (since it meant they were free from parental control.)  It was also named toga pura because it was white.
For the Romans dress was, like nowadays, an expression of social rank, gender and age. 

The topless bronze gladiatrix in Hamburg.

photo Alfonso Manas

Female gladiators existed!
A rarity, nevertheless, documented by Roman historians such as Dio Cassius (150-235 CE) who describes a festival organized by Nero for his mother (in which women fought). 
The same writer reports an event sponsored by the same emperor in the year 66 CE with Ethiopian women-gladiators in Pozzuoli in honor of the king of Armenia Tiridates.
Suetonius, another famous Roman historian and biographer (69-122 CE), describes games held under Domitian (88 CE) in which women fought against dwarfs!
Tacitus (Annales 15.32-33) reports that during a show in AD 63 some senators and noblewomen entered the arena to fight.
The satirical poet Juvenal describes Mevia hunting boars in the arena. 
Petronius (Satyricon) and Martial (Liber De Spectaculis) also refer to games involving women.
In the British Museum a marble relief found in Halicarnassus (Bodrum, Turkey) portrays 2 women gladiators nicknamed Achillia and Amazon. 

A bronze statuette, almost 2000 years old, in the Museum für Kunst und Gewerbein, in Hamburg,  has recently been interpreted as woman-gladiator, according to researcher Alfonso Manas, of Spain's University of Granada.  It could be a bare-chested woman brandishing a short, curved sword (sica).  The mysterious object she holds was previously identified as a strigil (used by Romans, who did not use soap, for scraping the body clean).
Manas is persuaded she is a gladiator for the pose:  typical of victorious gladiators.
Not surprising that she is topless:  women and men fought with bare chest.
Considering the audience was largely formed by men that caused a certain impact of course.

The scarcity of archaeological evidence depicting women gladiators however proves that women were rarely fighting. Such custom was banned by the emperor Septimus Severus (200 AD).