The authors conducted a study to describe the watermarks appearing in the text and map pages of the early Rome editions of Ptolemy’s Cosmography in order to date individual maps. They visited several institutions and libraries in Europe in person to study the atlases. Information and photographs concerning their atlases from institutions and libraries in the United States were collected by email correspondence. Information on some atlases was found directly on the internet. The conclusion is that each edition is characterized by its own specific watermarks. Photographs of all the watermarks found in each edition are displayed in this article.