Hundreds of protesters, including the infamous anarchists, gathered at Arsenal Park, Pittsburgh, on Sept. 24. When they attempted to march Downtown, they were met with a massive police contingent. Sonic cannons, OC gas and general mayhem ensued. Hundreds of protesters, including the infamous anarchists, gathered at Arsenal Park, Pittsburgh, on Sept. 24. When they attempted to march Downtown, they were met with a massive police contingent. Sonic cannons, OC gas and general mayhem ensued.