The donjon of Cathédrale Saint-Étienne d’Agde, built in 1173. Agde, France. Photo by Amber Maitrejean

The donjon of Cathédrale Saint-Étienne d’Agde, built in 1173. Agde, France. Photo by Amber Maitrejean

Tour César (Caesar’s Tower) is a medieval donjon in the UNESCO World Heritage town of Provins, France. The tower was probably built during the reign of Henry the Liberal (1152-1183), but a tower has occupied the location since 1137. The base of the donjon is square leading to an octagonal upper section with four turrets flanking the donjon. Provins, France. Photo by Amber Maitrejean

Tour César (Caesar’s Tower) is a medieval donjon in the UNESCO World Heritage town of Provins, France. The tower was probably built during the reign of Henry the Liberal (1152-1183), but a tower has occupied the location since 1137. The base of the donjon is square leading to an octagonal upper section with four turrets flanking the donjon. Provins, France. Photo by Amber Maitrejean

The donjon, enceinte and watchtowers of Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

The donjon, enceinte and watchtowers of Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Chateau Vincennes as viewed from atop the donjon. Vincennes, France. Photo by Amber Maitrejean

Chateau Vincennes as viewed from atop the donjon. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Paris as viewed from atop the donjon, the highest medieval fortified structure in Europe. Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Inmates kept track of the days/weeks/months while imprisoned in the donjon of Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Inmates kept track of the days/weeks/months while imprisoned in the donjon of Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

Prisoner graffiti in the donjon of Chateau Vincennes. Vincennes was used as a state prison numerous times from the Middle Ages up to the German Occupation and the Liberation. Some of its famous occupants include the Marquis de Sade, Diderot and Mirabeau. Vincennes, France. Photo by Amber Maitrejean

Prisoner graffiti in the donjon of Chateau Vincennes. Vincennes was used as a state prison numerous times from the Middle Ages up to the German Occupation and the Liberation. Some of its famous occupants include the Marquis de Sade, Diderot and Mirabeau. Vincennes, France. Photo by Amber Maitrejean

"Domus Dolorum" - "House of Pain", painted by a prisoner in the donjon of Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean

"Domus Dolorum" - "House of Pain", painted by a prisoner in the donjon of Chateau Vincennes. Vincennes, France. Photo by Amber Maitrejean