The fortress had also served as an Oflag in World War I .
Oflag XII - B was a German World War II prisoner - of - war camp for officers ( Offizierlager ) located in the citadel of Mainz , in western Germany .
The fortress had also served as an Offizierlager in World War I .
Oflag XII - B was a German World War II prisoner - of - war camp for officers ( Offizierlager ) located in the citadel of Mainz , in western Germany .