Short answers, pulled from the story.
About 230 Roman amphitheatres have been found across the area of the Roman Empire. Most remained concentrated in the Latin-speaking western half, while in the east spectacles were usually staged in theatres or stadia.
Roman amphitheatres were used for gladiator combats, venationes (animal slayings), and executions. Gladiatorial munera disappeared during the third century, while venationes survived until the sixth century.
The Colosseum in Rome, formally the Flavian Amphitheatre, is the largest Roman amphitheatre ever built. Its building dimensions are 188 by 156 meters, and it was completed and opened in 80 AD by Emperor Titus.
According to Jean-Claude Golvin, the earliest known stone amphitheatres are found in Campania, at Capua, Cumae, and Liternum, built toward the end of the second century BC. The amphitheatre of Pompeii, dated to shortly after 70 BC, is one of the oldest surviving examples and is also the oldest surviving Roman amphitheatre built with stone.
The last construction of a Roman amphitheatre is recorded in 523 in Pavia, built under Theodoric. After that, no further amphitheatres were built.
After gladiatorial games declined in the third century, amphitheatres were used for public executions and punishments. When even that purpose faded, many were repurposed as fortifications, Christian churches, or stripped for building material; the Colosseum became a Christian shrine in the 18th century.