The Stadium of Magnesia in modern-day Turkey was discovered in 2012.
The stadium, aligned on the north-south axis, was erected between two hills. Fifty-two stairs had to be ascended to reach its highest level and it could accommodate 30 thousand spectators. The stadium was 189 meters long.”
At the base of the stairs, the archaeologists discovered 129 so-called tropaion reliefs, showing armors, shields, and helmets of the enemies, to symbolise triumphs and victories.
These reliefs also suggest that gladiatorial fights were organised in the stadium. According to the inscriptions found there, the stadium was still in use in the 3rd century AD.
If you’re interested in learning more about the Ancient Greek city and its excavation progress, you can start on Wikipedia.