{{Short description|Ancient Roman masonry using irregular stones in a core of concrete}} {{Italics title}} {{refimprove|date=March 2026}} [[File:Arcate tempio di Giove.jpg|thumb|''Opus incertum'' on the Temple of Jupiter Anxur in Terracina, Italy]] '''''Opus incertum''''' ("irregular work") was an ancient Roman construction technique, using irregularly shaped and randomly placed uncut stones or fist-sized tuff<!--NOT tufa--> blocks inserted in a core of ''opus caementicium''.<ref name=DGRA>{{cite book |editor1-last=Smith |editor1-first=William |editor2-last=Wayte |editor2-first=William |editor3-last=Marindin |editor3-first=G.E |title=A DICTIONARY OF GREEK AND ROMAN ANTIQUITIES, V.1 |date=1890 |publisher=Oxford University |edition=Third |url=https://books.google.com/books?id=ziMtyNsj6kUC&q=%22Opus%20incertum%22 |access-date=March 9, 2026}}</ref>
Initially it consisted of more careful placement of the ''caementa'' (rock fragments and small stones mixed with concrete), making the external surface as plain as possible. Later the external surface became plainer still by reducing the amount of concrete and choosing more regular small stones. When the amount of concrete between stones is particularly reduced, it is defined as ''opus quasi reticulatum''. Used from the beginning of the 2nd century BC until the mid-1st century BC, it was later largely superseded by ''opus reticulatum''.
Vitruvius, in De architectura (''Ten Books on Architecture''), favours ''opus incertum'', deriding ''opus reticulatum'' as more expensive and structurally inferior, since cracks propagate more easily.
==See also== * Roman masonry – building techniques in Ancient Rome *{{annotated link|Roman concrete|aka=''Opus caementicium''}}
==References== {{Reflist}}
{{DEFAULTSORT:Opus Incertum}} Category:Ancient Roman construction techniques
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