The Nika riots (Greek: Στάση του Νίκα), or Nika revolt, took place over the course of a week in Constantinople in 532. It was the most violence Constantinople had ever seen to that point, nearly half the city being burned or destroyed.
The ancient Roman and Byzantine Empires had well-developed associations which supported the different factions (or teams) under which competitors in certain sporting events competed; this was particularly true of chariot racing. There were four major factional teams of chariot racing, differentiated by the colour of the uniform in which they competed. These were the Blues, the Reds, the Greens, and the Whites, although by the Byzantine era the only teams with any influence were the Blues and Greens. The emperor Justinian I was a supporter of the Blues.
The teams had aspects of street gangs and political parties, grouping people by social class and religion, and they frequently tried to affect the policy of the Emperors by shouting political demands between the races. The imperial forces and guards in the city could not keep order without the cooperation of the circus factions which were in turn backed by the powerful aristocratic families of the city: this included some families who believed they had a more rightful claim to the throne than Justinian.
Setting the stage for the revolt, in 531 some members of the Blues and Greens had been arrested for murder in connection with deaths that occurred during rioting after a recent chariot race. Relatively limited riots were not unknown at chariot races, similar to the mayhem that erupts after a soccer or basketball championship in modern times. The murderers were to be hanged, and most of them were. But on January 10, 532, two of them, a Blue and a Green, escaped and were taking refuge in the sanctuary of a church surrounded by an angry mob.
Justinian was nervous: he was in the midst of negotiating with the Persians over peace in the east, there was enormous resentment over high taxes, and now he faced a potential crisis in his city. Facing this, he declared that a chariot race would be held on January 13 and commuted the sentences to imprisonment. The Blues and Greens responded by demanding that the two men be pardoned entirely.
On January 13 a tense and angry populace arrived at the Hippodrome for the races. The Hippodrome was next to the palace complex and thus Justinian could watch from the safety of his box in the palace and preside over the races. The crowd from the start had been hurling insults at Justinian. By the end of the day, at race 22, the partisan chants had changed from "Blue" or "Green" to a unified "Nika" (a Greek exhortation meaning to "win", "conquer", or "achieve victory"), and the crowds broke out and began to assault the palace. For the next five days the palace was under virtual siege.
Some of the senators saw this as an opportunity to overthrow Justinian, as they were opposed to his new taxes and his lack of support for the nobility. The rioters, now armed and probably controlled by their allies in the Senate, also demanded that Justinian dismiss the prefect John the Cappadocian, who was responsible for tax collecting, and the quaestor Tribonian, who was responsible for rewriting the legal code. They then declared a new emperor, Hypatius, who was a nephew of Emperor Anastasius I.
Justinian considered fleeing, but his wife Theodora convinced him to stay in the city. Justinian had his generals Belisarius and Mundus suppress the revolt on January 18, which they did with much bloodshed by trapping the rebels in the Hippodrome. About thirty thousand rioters were reportedly killed. Justinian also had Hypatius executed and exiled the senators who had supported the riot.
The riots in fiction
Procopius, "Justinian Suppresses the Nika Revolt, 532", from the Internet Medieval Sourcebook.
J. B. Bury, "The Nika Revolt", chapter XV part 5 from History of the Later Roman Empire (1923).