Despite numerous and detailed studies of the jets of Active Galactic Nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet-components is one of the most prominent unsolved problems as is the launching mechanism of jets in AGN. An in-depth investigation of long-term archival VLBI and multi-wavelength data (several decades) in combination with the application of theoretical models allows detailed studies of the overall properties of jets. This enables us to discriminate between motion scenarios and to derive a more physical understanding of the nature and and origin of jets in general. We will present and discuss recent results.<p>

In collaboration with: S.-J. Qian, E. Kun, M. Karouzos, J. Roland, L. Gergely, M. Aller, H. Aller, W. Steffen, A. Witzel, et al.