The Roman Amphitheater in Trier is designated as part of the Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier UNESCO World Heritage Site. The arena, built in the 2nd century A.D. for cruel games with gladiators and animals, had a seating capacity of about 20,000. When you enter the premises you walk through the ruins of the entrance gate. This was used as a quarry in the Middle Ages. The arena itself is surrounded by a protecting wall with openings for animal cages. Underneath the arena is a vast cellar where, in Roman times, prisoners sentenced to death were kept alongside exotic wild animals like African lions or Asian tigers.References:
The Amphitheatre of the Three Gauls was part of the federal sanctuary of the three Gauls dedicated to the cult of Rome and Augustus celebrated by the 60 Gallic tribes when they gathered at Lugdunum (Lyon). The amphitheatre was built at the foot of the La Croix-Rousse hill at what was then the confluence of the Rhône and Saône.
Excavations have revealed a basement of three elliptical walls linked by cross-walls and a channel surrounding the oval central arena. The arena was slightly sloped, with the building"s south part supported by a now-vanished vault. The arena"s dimensions are 67,6m by 42m. This phase of the amphitheatre housed games which accompanied the imperial cult, with its low capacity (1,800 seats) being enough for delegations from the 60 Gallic tribes.
The amphitheatre was expanded at the start of the 2nd century. Two galleries were added around the old amphitheatre, raising its width from 25 metres to 105 metres and its capacity to about 20,000 seats. In so doing it made it a building open to the whole population of Lugdunum and its environs.