Stephan's areas of specialization include interdisciplinary archaeological research in the first and second millennia AD, medieval settlement and landscape archaeology, urban topography and architectural history, renaissance material culture (especially ceramics, glass, and oven tiles), economic history (especially pottery, metallurgy and glass production), and archaeometry.

[7] Initially, Stephan and his team thought they had found a small, squarish building, but in 2004, the site was covered by brush,[8] later cleared away by the local historical society, which supports the project.

[4] The German state of Lower Saxony purchased the castle at Nienover in 2005, later selling it to Mireille van Meer, a Dutch horse breeder.

[9] Stephan, who spent twelve years researching and excavating the site, criticized Hartmut Möllring (CDU), state finance minister, for selling the castle at a "fire sale price" without bothering to secure the rights to continue the scientific work to its conclusion.

[2] The new owner prohibited excavation of a well 40 meters (130 ft) deep, despite private funding, including that of Lower Saxony's former Minister of Science and Culture, Thomas Oppermann.