Built around AD 100 and capable of holding 20,000 spectators, Trier's Roman Amphitheatre lies just beyond the medieval city wall. The arena itself is remarkably intact — the protective perimeter wall, the arched entrance, and the underground service level all survive. The stone seating was dismantled for building material in the 13th century, but the acoustics are still exceptional: the amphitheatre is used for open-air concerts today.
The underground level is the most compelling part of the visit: a labyrinth of tunnels, chambers, and animal pens beneath the arena floor, where prisoners condemned "ad bestias" (to the beasts) waited alongside lions and tigers imported from Africa and Asia. A moveable platform raised them into the arena for the spectacle above.
Nearby, an odd curve in the street beside St. Agritius Church marks the far turning-point of a Roman chariot-racing circuit, comparable in size to the Circus Maximus in Rome — nothing else is visible, but the ghost of the course can be traced in the street plan.