One of the basic principles of historical scholarship is the critical reading of sources, also known as ‘source criticism’. The term ‘critical’, or ‘criticism’ does not necessarily have a negative meaning here. Rather, it is about questioning a source at hand. What are the external characteristics of the document? Is it an original? Who created it? When? For what reason? In what context? What does the content say? Is it trustworthy? Only then can a document be properly classified. This principle is not only applied to written documents, but also to pictures, cartoons, or audiovisual documents, for example. Here, we analyse some sources from or about East Belgium.