One branch of my family line (Rodenhouse<-Rothuizen<-Rothuis or Rottheus) runs out of references with the birth of Wilhelm Rottheus in 1721, with a separate comment that he was living in Stadtlohn, Germany. Those descendants generally lived in Gelderland after that. I've looked at some German databases, but can't find either Rottheus or Rothuis.
There is a separate Rothuis line that is from the Frisian Islands, but is not related to my line.
Any suggestions as to where to look for more information on Wilhelm Rottheus (1721) and his family?