Understanding simple electric DC circuits often represents a great challenge to many students in lower secondary schools. As a result, students' knowledge of this subject is often dominated by alternative conceptions, even after instruction. One of the reasons for these learning difficulties is the intangibility of key physical quantities and concepts of electric circuits such as the electric potential or the electric current. A potentially effective way of making circuits more accessible to students in introductory electricity lessons represents the use of analogies or models. However, as a brief review shows, there is no single analogy or model that is ideally suited to foster an understanding of all key aspects of simple DC circuits. In order to address this issue and help learners develop a mental model of circuits, a new analogical simulation of simple electric circuits was developed. The simulation is suited for use in combination with the bike chain and the air pressure analogy and aims to support students' development of a qualitative understanding of potential difference and current in circuits as well as a treatment of circuits as a connected system. Teachers and students can access the 3D simulation free of charge using a modern browser via www.marblemodel.com.