Those near the Colosseum during the battle could hear the sounds of explosions setting off one after another. The place had a lot of formations put around it, but Talho never bothered to put a sound formation on it as the sounds of battle and excitement of the audience could work to entice more people to pay to enter.
Right now, however, the only thing people could hear was what sounded like a war happening inside the arena. And that by itself wasn't a wrong way to put it.
Those sounds were, of course, tied to Mares and Impact's battle. Done with their warm-up, the two exchanged hit after hit, causing shockwaves that were even stronger than those made by some explosions.
If it wasn't for the formations protecting the audience, the tremors alone would be equivalent or worse to an earthquake.