At this time, Abbot Heinrich vested Counts Diether and Eberhardt I of Katzenelnbogen with the villages of Roßdorf and Gundernhausen.

The forces of the Holy Roman Empire and Sweden opposed each other in the region, each in turn laying waste to and scavenging the entire countryside and heavily decimating the population.

The coat of arms is based on the seal of the combined village court of Roßdorf and Gundernhausen.

An imprint of this seal can be found on the so-called "Mansfeld Catalogue of Damages" from 1625, which is kept in the National Archive in Darmstadt.

This Catalogue lists the losses suffered by the subjects of the Counts of Katzenelnbogen during the Thirty Years' War.

Roßdorf is also the headquarters of the Gesellschaft zur wissenschaftlichen Untersuchung von Parawissenschaften (GWUP; "Society for the Scientific Investigation of Parasciences"), the European Council of Skeptical Organisations (ECSO) and the Center for Inquiry-Europe.

In addition, a number of bus routes serve Roßdorf: The rail line between the "Darmstadt Ost" and "Bessunger Forsthaus" halts is still occasionally used for historical train rides.