As powerful economic and cultural centers, fortified sites played an important role in early medieval society. In Central Europe, early medieval fortified site research has been an essential topic for several generations. However, gradual changes in the landscape are a threat to these cultural heritage monuments. The main task of this paper was to compare the previous results from archaeological excavations with new data acquired by geophysical methods. The presented study is based on the three methods widely used in archaeology: magnetometry, ground-penetrating radar, and electrical resistivity tomography. New surveys provide information about the internal structure and the state of preservation of the fortifications in a non-destructive way. Comparison of the results encourages the evaluation of archaeological excavation and helps determine the suitability and effectiveness of geophysical methods in specific natural conditions.

Regions densely populated with archaeological monuments pose significant challenges for construction investors and archaeologists during the planning stages of major construction projects. Recognising the archaeological potential of these areas is crucial for planning effective rescue excavations, which have become a standard procedure in construction. This study explores the utility of non-invasive prospection techniques, including artefact field surveys, multispectral imaging, and magnetic surveys, in assessing the area chosen for the I/16 Slaný–Velvary road construction. We specifically focused on the contributions these methods make towards understanding the archaeological context of the proposed construction site. The findings from the magnetic survey were compared with the results of actual archaeological excavations. Through manual visual analysis and statistical spatial correlation, we assessed the effectiveness of the magnetic survey. The ability of magnetic survey to locate different types of archaeological objects proved to be dependent on various factors. The variability of the environmental setting, particularly pedological and geological conditions, is essential. However, the modern anthropogenic impact and the very nature of individual archaeological objects, especially their dimensions, also play an essential role.