The massive and majestic Colosseum, ancient Rome's most famous monument, was begun by the Flavian emperor Vespasian (AD 7-79) in AD 72 and inaugurated eight years later with a program of games and shows lasting 100 days. More than 70,000 spectators could sit within the arena's 573-yard circumference, which had marble facing, hundreds of statues for decoration, and a velarium -- an ingenious system of sail-like awnings rigged on ropes manned by imperial sailors -- to protect the audience from the sun and rain. Before the imperial box, gladiators would salute the emperor and cry, "Ave, imperator, morituri te salutant" ("Hail, emperor, men soon to die salute you"); it is said that when one day they heard the emperor Claudius respond, "Or maybe not," they were so offended that they called a strike.

Originally known as the Flavian Amphitheater, it took the name Colosseum after a truly colossal gilt bronze statue of Nero that stood nearby. Gladiator combat and staged animal hunts ended by the 6th century. The arena later served as a quarry from which materials were looted to build Renaissance churches and palaces. Finally, it was declared sacred by the Vatican in memory of the many Christians believed martyred here. (Scholars now maintain that Christians met their death elsewhere.) During the 19th century, romantic poets lauded the glories of the ruins when viewed by moonlight. Now its arches glow at night with mellow golden spotlights -- less romantic, perhaps, but still impressive. COST: EUR8, includes Palatine Hill admission; EUR20, multisight ticket; reservation fee EUR1.50.