Abstract: In this paper we present some preliminary results concerning a real-time visualisation system for densely populated urban environments. In order to be able to render the large number of humans, we developed a method based on Image-Based Rendering techniques. To allow them to move freely in the city while avoiding collusions against the environment and other humans, we developed a simplified collision test that makes use of the graphics hardware to quickly generate a discretization of the environment. Although our research is at an early stage, the results are already quite promising; we are able to render in real-time a virtual city with thousands of walking humans on a standard PC. Several avenues for further investigation are finally proposed.