Recently, we have identified a small number of extended radio sources that consist of two double-lobed radio sources, which axe well aligned and centered on a common nucleus. We have called these 'Double-double radio galaxies' (DDRGs). The observed structures strongly suggest interrupted central activity as the origin of these sources. We have developed a model based on this assumption with which we are able to explain several observed properties. Since the inner structures of the DDRGs advan...