Franz Anton Mehlem was located in Bonn, Northrhine-Westphalia. He was among the manufacturers experimenting with different mixtures to give their earthenware products a more porcelain-like look and feel and his was one of the companies leading that technology and extremely successful during 1880 to 1910.
Quite a lot of Mehlem products were made on special order or were made based on designs from famous artists or teachers at art and craft academies e.g. Ernst Aufseeser, Wilhelm Neuhauser or Peter Behrens. The company was taken over by Villeroy and Bosch in 1920 and the company headquarters were finally demolished in 1931.
This is an example piece which shows the castle detail on the base and is listed for sale at �80.
http://www.trocadero.com/Farthings/items/29042 3/en5.html