Reconfigurable intelligent surfaces (RISs) are considered a promising technology for boosting the coverage and for enhancing the spectral efficiency of wireless systems, as well as for taming the wireless environment. The potential benefits of RISs are currently being analyzed and various approaches are being proposed to address some challenges for their integration in wireless networks. Currently available studies to quantify the potential gains of deploying RISs in wireless networks are limited to simple network topologies, while no system-level assessments have been reported to date. Network-level, e.g., on the scale of hundreds of square meters, simulations are, however, the first step to quantify the actual value of emerging technologies and the steppingstone before considering large scale system-level experimental evaluations and network deployments. Towards this direction, this article reports the first system-level simulation results and analysis of an RIS deployment in a typical urban city that is served by a fifth-generation cellular network. The obtained system-level simulation results unveil that the benefits of RISs vary depending on the operating frequency and the size of the surfaces. Specifically, we investigate the performance improvement that RISs can provide, in terms of outdoor and indoor coverage and ergodic rate, when deployed in mid (C-band) and high (millimeter-wave) frequency bands. For example, the obtained results unveil that the deployment of RISs enhances the coverage of cell-edge users from 77% to 95% in the C-band and from 46% to 95% in the millimeter-wave band.