That is, when Romans had their cell phones turned on. Telecom Italia, Italy's main telephone operator, has partnered with the Massachusetts Institute of Technology on a real-time mapping system that tracks how people move in urban spaces.
This part looks interesting:
Real Time Rome is also being used to figure out how tourists in Rome move throughout the city and can show where spikes in the volume of calls happen. One sample image from the project, for example, shows spiked cell phone usage around Olympic Stadium in Rome and the Vatican during Madonna's infamous on-the-cross appearance last month. Another shows Rome's population movement around the time of Italy's World Cup win.
Of course, there is the usual talk about personal privacy and such. I don't really carry a cell phone with me a whole lot, so such issues are hardly a concern. Besides, what is very interesting about tracking Romans sitting in gridlock? Hmmm?