Opus Incertum: No it's not a Harry Potter spell

 

While walking around Pompeii, we saw many different types of walls and wall building techniques. The one that intrigued me the most was the opus incertum technique. How do such seemingly random placed stones last 2000 years? Was there a method to the madness? When I found out that this technique is the most commonly found at the site of Pompeii it made me wonder if the builders at the time knew how successful it would be or if they just thought it was the easiest.[1] Based on surveys done by Auterio et al., many consistencies were found within these walls: 1) the stones were not aligned in any way but the smaller ones were used to fill gaps between larger ones 2) lava, travertine and foam lava stones were most commonly used 3) thickness of the walls was between 0.35-0.48 m.[2] However, irregular and discontinues texture is not necessarily the hidden superhero I had hoped for as it in fact does not assure the compactness of the material or monolith behavior.[3] Due to the random placement of stone it does not allow an even distribution of weight and can cause the weakest parts of the wall to crack under pressure, literally.[4] Although it is most common, studies show that opus incertum is not the best option for longevity under stress. Tune in next week to find out what technique might be a better candidate.

Example of an original opus incertum wall in Pompeii.

Image credits: Alayna Krueger

Another example of opus incertum in Pompeii, this one was once covered by plaster.

Image credits: Alayna Krueger

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[1] Autiero, Francesca, Giuseppina De Martino, Marco Di Ludovico, and Andrea Prota. “Mechanical Performance of Full-Scale Pompeii-like Masonry Panels.” Construction and Building Materials 251 (August 2020). doi: 10.1016/j.conbuildmat.2020.118964.

[2] Auterio et al., 4.

[3] Santini, Silvia, Marina Cogotti, Carlo Baggio, Valerio Sabbatini, and Claudio Sebastiani. “Field Testing for Structural Behavior of a Stratified Monumental Complex over Time: Palazzo Colonna-Barberini and Templum Fortunae Praeneste.” Case Studies in Construction Materials 18 (July 2023). doi: 10.1016/j.cscm.2023.e02152.

[4] Auterio et al., 12. 

Bibliography 

Autiero, Francesca, Giuseppina De Martino, Marco Di Ludovico, and Andrea Prota. “Mechanical Performance of Full-Scale Pompeii-like Masonry Panels.” Construction and Building Materials 251 (August 2020). doi: 10.1016/j.conbuildmat.2020.118964.

Santini, Silvia, Marina Cogotti, Carlo Baggio, Valerio Sabbatini, and Claudio Sebastiani. “Field Testing for Structural Behavior of a Stratified Monumental Complex over Time: Palazzo Colonna-Barberini and Templum Fortunae Praeneste.” Case Studies in Construction Materials 18 (July 2023). doi: 10.1016/j.cscm.2023.e02152.