The Roman Limes with a length of 550 km is the largest archaeological site of Europe as well as the largest monument of the Roman period. In July 2005 it was decided that the Limes and its interrelated archaeological sites, together with Hadrian's Wall in England, would be a component of a ‘Trans-National World Heritage Site’ taking the name ‘Frontiers of the Roman Empire’. From that point it was necessary to minimize and/or to avoid archaeological excavation. Further research on such sites is mainly limited to the application of non-destructive techniques. Among other geophysical tools, magnetometry, based on the rock magnetic knowledge turned out to be a highly suitable method. Two examples that allowed verification and completion of old maps of the Reichs-Limes-Kommission will be shown here; these projects exemplify geophysical work on the Bavarian Limes. At the site of Oberhochstatt we discovered the exact location and determined information on the size and orientation of the fort that previous searches for a long time had failed to find. At Theilenhofen we were able to complete the map of the whole fort with all fortification ditches and the water supply, to verify the troop level and to confirm the former fort on which is superimposed the traces of the Roman vicus. Copyright © 2010 John Wiley & Sons, Ltd.