circus [Lat.,=ring, circle], historically, the arena associated with the horse and chariot races and athletic contests known in ancient Rome as the Circensian games. The Roman circus was a round or oval structure with tiers of seats for spectators, enclosing a space in which the races, games, and gladiatorial combats took place. Underneath were dressing rooms, dens for wild beasts, and rooms where properties were stored. The Circus Maximus, presumably built in the reign of Tarquin I (c.616-c.578 B.C.), and rebuilt by Julius Caesar, was reported by Pliny in his Natural History to have a capacity of 250,000, though this figure is suspiciously large. Other famous circi of Rome were the Circus Flaminius (221 B.C.); the Circus Neronis, of Caligula and Nero, at which many Christians perished; and the Circus Maxentius. The circus of Septimius Severus at Constantinople and many others were often scenes of riot and bloodshed between factions of charioteers. The games, aside from races, were brutal and bloody, and for this reason the Greeks, even under Roman domination, never really accepted the circus.

The modern circus, which originated in performances of equestrian feats in a horse ring strewn with sawdust, dates from the closing years of the 18th cent. The circus is traditionally a nomadic tent show, with trained animals, acrobats, and clowns. The main tent, known as the big top, is often surrounded by various concessions and sideshows with "freaks" and wild animals. Even before 1830, traveling circuses were common in the United States and in England. After 1873 two rings were used in the main tent and the three-ring circus, as we know it today, was initiated by James A. Bailey. The most celebrated circus in America was "The Greatest Show on Earth" of P. T. Barnum, which, in merging with Bailey's, became Barnum and Bailey's. On Bailey's death in 1907 the circus was purchased by Ringling Brothers, and in 1919 the two circuses were combined. Since 1969, Ringling Brothers has had two large circuses on tour that play mostly indoors and visit almost every major U.S. city annually.

The traveling circus, in its heyday from 1880 to 1920, declined in the 1950s and 60s. By the 1980s, however, more than 30 circuses were touring the United States and Canada. Outstanding among contemporary circuses are two small and sophisticated shows, the New York City-based Big Apple Circus and the Montreal-based Cirque du Soleil. The latter is the most elaborate and best known exponent of the form called cirque nouveau. A type of modern circus without animal acts, it is characterized by a mixture of traditional circus arts with poetic spectacle, music, and dance and is practiced by a number of European and Canadian troupes.

Entertainment or spectacle featuring animal acts and human feats of daring. The modern circus was founded in England in 1768 by the bareback rider Philip Astley (1742–1814), who built stands around his performance ring and opened Astley's Amphitheatre. One of his riders later established the Royal Circus (1782), the first modern use of the term. The first U.S. circus opened in Philadelphia in 1793. Horse acts were later joined by wild-animal acts. After the invention of the flying trapeze by Jules Léotard (1859), aerial acts were featured. P.T. Barnum expanded the traditional circus by adding two rings to create the three-ring circus (1881) and augmented it with sideshow performers. Circuses traveled throughout the U.S., Europe, and Latin America, performing in a tent (the Big Top) into the 1950s. Today circuses usually perform in permanent buildings, though small troupes still travel with tents in some regions. By the late 20th century, notable circuses also had developed in Africa, India, Spain, Brazil, and Mexico. Perhaps the most innovative trend in circuses at the turn of the 21st century was the establishment of companies such as the Cirque du Soleil; these companies employed no animals, instead emphasizing acts of human skill and daring and integrating elements of contemporary music and dance into the overall performance.

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