Opus reticulatum (also known as reticulate work) is a facing used for concrete walls in Roman architecture from about the first century BCE to the early first century CE. They were built using small pyramid-shaped tuff, a volcanic stone embedded into a concrete core. Reticulate work was also combined with a multitude of other building materials to provide polychrome colouring and other facings to form new techniques. Opus reticulatum was generally used in central and southern Italy with the exception being its rare appearance in Africa and Jericho. This was because of tuff's wider availability and ease of local transport in central Italy and Campania compared to other regions. Reticulate work developed in response to the advent of opus caementicium and its predecessor, opus incertum. This was to accommodate both the new building material and the growing demands of urbanisation in Rome through the creation of opus reticulatum, a method more uniform and accessible to unskilled labourers. The need for quicker and easier techniques led to a decline in popularity allowing for the rise of brickwork as a more convenient alternative, especially after the Great Fire of 64 CE. Opus reticulatum is important for understanding the choices the Romans made with their architecture while keeping in mind the architectural restraints and changes in their circumstances. Reticulate work can also provide evidence of cross-cultural exchange between Rome and its correspondents through its usage outside of central and southern Italy. Further, a written account from Vitruvius shows a Roman opinion on opus reticulatum and its significance in Roman culture. Along with other facings, the technique is also important for dating buildings in modern scholarship where there is an absence in explicit evidence to date the construction.
Construction and use
Opus reticulatum was built through laying a repetitive sequence opus caementicium, caementa and small pyramid shaped tuff to form a net-like pattern. The uniform shape of the stones allowed for easy assemblage which Rome used to delegate work to unpaid labour with little training to construct architecture using the facing. The technique provided a greater focus on shifting the workload to preparation and concrete making. The use of opus reticulatum followed utilitarian characteristics common with Roman architecture where they prioritised both practical and aesthetic sensibilities to build their constructions. Reticulate work was typically used for a variety of architecture including walls, aqueducts among other works. They could be easily stylised with a multitude of material including limestone, lava, and bricks to produce polychrome colouring. Other facings could also be used to form opus mixtum. This was because opus reticulatum’s reliance on uniform tuff blocks meant customisation was easily achieved. The Romans produced lines, complex, figures and letter which were covered with a veneer particularly in Rome during the Augustus’s reign. Such a covering was possibly a later addition or a request from the commissioner according to Jean Pierre Adam. However, Fikret Yegül and Diane Favro do suggest they were always intended to be covered with a decorative veneer which would then be patterned and painted even replicating expensive marble. With Roman craftsmen developing an interest to show uncovered polychromatic colouring at the start of the Augustan period where diverse usage of building materials emerged.
Material While opus reticulatum used tuff to face opus caementicium core, Roman architects did not use the same tuff throughout their history changing which ones they used depending on their strength. Reticulate work used Tufo Lionato, a tawny orange coloured tuff from the Aniene River. This stone has been cited by Marie Jackson and Fabrizio Marra as having perfected opus reticulatum and opus mixtum during the height of its use. Another tuff used was peperino, a dark grey coloured stone used from the end of the second century BCE.
Location The architectural technique was typically found in central and southern Italy. This is because tuff is predominant in such areas because of their volcanic environment. Further, they also lacked smooth stones like limestone or marble and instead had to rely on volcanic stones for their architecture. The Romans tend not to change core building materials of the places they conquered but rather adapted and used what was readily available to them. This is evident with other techniques such as opus vittatum which used limestone and tuff was localised to central and northern Italy particularly because of the existence of the former in the region. The Romans did this for practical reasons as building products like stone were difficult to transport long distances because of their weight and had to be partially cut to decrease weight before being sent to the construction site. This was not the case for tuff, which could be easily transported and used throughout central Italy and Campania where it became a common building stone.
While opus reticulatum was typically found in central and southern Italy, the technique had rare appearances in Africa forming another facing called opus africanum. The technique used vertical stone piers filled with rubble mortar which was then faced with unshaped stones, rectangular blocks, or opus reticulatum. A notable example includes a building in Bulla Regia, a Roman town in modern-day Jendouba, Tunisia. Another use of reticulate work outside of Italy was the client king, Herod's winter palace in Jericho. This was among some of the many techniques used for his architectural projects during the late first century BCE.
Development
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