Colosseum is a massive RF and computational facility that emulates wireless signals (with granularity at the RF signal level) traversing space and reflecting off multiple objects and obstacles as they travel from transmitters to receivers. Allowing 256 x 256 100 MHz RF channel emulations, with USRP X310 radio nodes in the loop interacting in over 65,000+ channels at the same time, Colosseum can create virtual worlds, as if the radios are operating in an open field, urban area, shopping mall, or a desert, by generating more than 52 terabytes of data per second. Colosseum enables full stack wireless networking research from applications down to the physical layer at scale - with up to 256 interacting radios.